postfix настройка smtp аутентификации

Postfix configuration parameters

The Postfix main.cf configuration file specifies a very small
subset of all the parameters that control the operation of the
Postfix mail system. Parameters not explicitly specified are left
at their default values.

The remainder of this document is a description of all Postfix
configuration parameters. Default values are shown after the
parameter name in parentheses, and can be looked up with the
postconf -d” command.

Note: this is not an invitation to make changes to Postfix
configuration parameters. Unnecessary changes are likely to impair
the operation of the mail system.


(default: postmaster)

The recipient of undeliverable mail that cannot be returned to
the sender. This feature is enabled with the notify_classes
parameter.


(default: 450)

The numerical Postfix SMTP server response code for
an access(5) map “defer” action, including “defer_if_permit
or “defer_if_reject“. Prior to Postfix 2.6, the response
is hard-coded as “450”.

Do not change this unless you have a complete understanding of RFC 5321.

This feature is available in Postfix 2.6 and later.


(default: 554)

The numerical Postfix SMTP server response code for
an access(5) map “reject” action.

Do not change this unless you have a complete understanding of RFC 5321.


(default: 12h)

The amount of time between verify(8) address verification
database cleanup runs. This feature requires that the database
supports the “delete” and “sequence” operators. Specify a zero
interval to disable database cleanup.

After each database cleanup run, the verify(8) daemon logs the
number of entries that were retained and dropped. A cleanup run is
logged as “partial” when the daemon terminates early after “postfix
reload
“, “postfix stop“, or no requests for $max_idle
seconds.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).

This feature is available in Postfix 2.7.


(default: $default_transport)

Overrides the default_transport parameter setting for address
verification probes.

This feature is available in Postfix 2.1 and later.


(default: $local_transport)

Overrides the local_transport parameter setting for address
verification probes.

This feature is available in Postfix 2.1 and later.


(default: see “postconf -d” output)

Lookup table for persistent address verification status
storage. The table is maintained by the verify(8) service, and
is opened before the process releases privileges.

The lookup table is persistent by default (Postfix 2.7 and later).
Specify an empty table name to keep the information in volatile
memory which is lost after “postfix reload” or “postfix
stop
“. This is the default with Postfix version 2.6 and earlier.

Specify a location in a file system that will not fill up. If the
database becomes corrupted, the world comes to an end. To recover,
delete (NOT: truncate) the file and do “postfix reload“.

Postfix daemon processes do not use root privileges when opening
this file (Postfix 2.5 and later). The file must therefore be
stored under a Postfix-owned directory such as the data_directory.
As a migration aid, an attempt to open the file under a non-Postfix
directory is redirected to the Postfix-owned data_directory, and a
warning is logged.

Examples:

address_verify_map = hash:/var/lib/postfix/verify
address_verify_map = btree:/var/lib/postfix/verify

This feature is available in Postfix 2.1 and later.


(default: yes)

Enable caching of failed address verification probe results. When
this feature is enabled, the cache may pollute quickly with garbage.
When this feature is disabled, Postfix will generate an address
probe for every lookup.

This feature is available in Postfix 2.1 and later.


(default: 3d)

The time after which a failed probe expires from the address
verification cache.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.1 and later.


(default: 3h)

The time after which a failed address verification probe needs to
be refreshed.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).

This feature is available in Postfix 2.1 and later.


(default: see “postconf -d” output)

A safety limit that prevents address verification requests from
overwhelming the Postfix queue. By default, the number of pending
requests is limited to 1/4 of the active queue maximum size
(qmgr_message_active_limit). The queue manager enforces the limit
by tempfailing requests that exceed the limit. This affects only
unknown addresses and inactive addresses that have expired, because
the verify(8) daemon automatically refreshes an active address
before it expires.

This feature is available in Postfix 3.1 and later.


(default: normal: 3, overload: 1)

How many times to query the verify(8) service for the completion
of an address verification request in progress.

By default, the Postfix SMTP server polls the verify(8) service
up to three times under non-overload conditions, and only once when
under overload. With Postfix version 2.5 and earlier, the SMTP
server always polls the verify(8) service up to three times by
default.

Specify 1 to implement a crude form of greylisting, that is, always
defer the first delivery request for a new address.

Examples:

# Postfix ≤ 2.6 default
address_verify_poll_count = 3
# Poor man's greylisting
address_verify_poll_count = 1

This feature is available in Postfix 2.1 and later.


(default: 3s)

The delay between queries for the completion of an address
verification request in progress.

The default polling delay is 3 seconds.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: 31d)

The time after which a successful probe expires from the address
verification cache.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.1 and later.


(default: 7d)

The time after which a successful address verification probe needs
to be refreshed. The address verification status is not updated
when the probe fails (optimistic caching).

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.1 and later.


(default: $relay_transport)

Overrides the relay_transport parameter setting for address
verification probes.

This feature is available in Postfix 2.1 and later.


(default: $relayhost)

Overrides the relayhost parameter setting for address verification
probes. This information can be overruled with the transport(5) table.

This feature is available in Postfix 2.1 and later.


(default: $double_bounce_sender)

The sender address to use in address verification probes; prior
to Postfix 2.5 the default was “postmaster”. To
avoid problems with address probes that are sent in response to
address probes, the Postfix SMTP server excludes the probe sender
address from all SMTPD access blocks.

Specify an empty value (address_verify_sender =) or <> if you want
to use the null sender address. Beware, some sites reject mail from
<>, even though RFCs require that such addresses be accepted.

Examples:

address_verify_sender = <>
address_verify_sender = postmaster@my.domain

This feature is available in Postfix 2.1 and later.


(default: $sender_dependent_default_transport_maps)

Overrides the sender_dependent_default_transport_maps parameter
setting for address verification probes.

This feature is available in Postfix 2.7 and later.


(default: $sender_dependent_relayhost_maps)

Overrides the sender_dependent_relayhost_maps parameter setting for address
verification probes.

This feature is available in Postfix 2.3 and later.


(default: 0s)

The time between changes in the time-dependent portion of address
verification probe sender addresses. The time-dependent portion is
appended to the localpart of the address specified with the
address_verify_sender parameter. This feature is ignored when the
probe sender addresses is the null sender, i.e. the address_verify_sender
value is empty or <>.

Historically, the probe sender address was fixed. This has
caused such addresses to end up on spammer mailing lists, and has
resulted in wasted network and processing resources.

To enable time-dependent probe sender addresses, specify a
non-zero time value. Specify a value of at least several hours,
to avoid problems with senders that use greylisting. Avoid nice
TTL values, to make the result less predictable.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.9 and later.


(default: verify)

The name of the verify(8) address verification service. This service
maintains the status of sender and/or recipient address verification
probes, and generates probes on request by other Postfix processes.


(default: $transport_maps)

Overrides the transport_maps parameter setting for address verification
probes.

This feature is available in Postfix 2.1 and later.


(default: $virtual_transport)

Overrides the virtual_transport parameter setting for address
verification probes.

This feature is available in Postfix 2.1 and later.


(default: see “postconf -d” output)

The alias databases for local(8) delivery that are updated with
newaliases” or with “sendmail -bi“.

This is a separate configuration parameter because not all the
tables specified with $alias_maps have to be local files.

Examples:

alias_database = hash:/etc/aliases
alias_database = hash:/etc/mail/aliases

(default: see “postconf -d” output)

The alias databases that are used for local(8) delivery. See
aliases(5) for syntax details.
Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.
Note: these lookups are recursive.

The default list is system dependent. On systems with NIS, the
default is to search the local alias database, then the NIS alias
database.

If you change the alias database, run “postalias /etc/aliases
(or wherever your system stores the mail alias file), or simply
run “newaliases” to build the necessary DBM or DB file.

The local(8) delivery agent disallows regular expression substitution
of $1 etc. in alias_maps, because that would open a security hole.

The local(8) delivery agent will silently ignore requests to use
the proxymap(8) server within alias_maps. Instead it will open the
table directly. Before Postfix version 2.2, the local(8) delivery
agent will terminate with a fatal error.

Examples:

alias_maps = hash:/etc/aliases, nis:mail.aliases
alias_maps = hash:/etc/aliases

(default: alias, forward)

Restrict local(8) mail delivery to external commands. The default
is to disallow delivery to “|command” in :include: files (see
aliases(5) for the text that defines this terminology).

Specify zero or more of: alias, forward or include,
in order to allow commands in aliases(5), .forward files or in
:include: files, respectively.

Example:

allow_mail_to_commands = alias,forward,include

(default: alias, forward)

Restrict local(8) mail delivery to external files. The default is
to disallow “/file/name” destinations in :include: files (see
aliases(5) for the text that defines this terminology).

Specify zero or more of: alias, forward or include,
in order to allow “/file/name” destinations in aliases(5), .forward
files and in :include: files, respectively.

Example:

allow_mail_to_files = alias,forward,include

(default: no)

Allow a sender or recipient address to have `-‘ as the first
character. By
default, this is not allowed, to avoid accidents with software that
passes email addresses via the command line. Such software
would not be able to distinguish a malicious address from a
bona fide command-line option. Although this can be prevented by
inserting a “–” option terminator into the command line, this is
difficult to enforce consistently and globally.

As of Postfix version 2.5, this feature is implemented by
trivial-rewrite(8). With earlier versions this feature was implemented
by qmgr(8) and was limited to recipient addresses only.


(default: yes)

Enable the rewriting of the form “user%domain” to “user@domain”.
This is enabled by default.

Note: as of Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true:

To get the behavior before Postfix version 2.2, specify
local_header_rewrite_clients = static:all”.

Example:

allow_percent_hack = no

(default: no)

Forward mail with sender-specified routing (user[@%!]remote[@%!]site)
from untrusted clients to destinations matching $relay_domains.

By default, this feature is turned off. This closes a nasty open
relay loophole where a backup MX host can be tricked into forwarding
junk mail to a primary MX host which then spams it out to the world.

This parameter also controls if non-local addresses with sender-specified
routing can match Postfix access tables. By default, such addresses
cannot match Postfix access tables, because the address is ambiguous.


(default: empty)

A list of non-default Postfix configuration directories that may
be specified with “-c config_directory” on the command line (in the
case of sendmail(1), with the “-C” option), or via the MAIL_CONFIG
environment parameter.

This list must be specified in the default Postfix main.cf file,
and will be used by set-gid Postfix commands such as postqueue(1)
and postdrop(1).

Specify absolute pathnames, separated by comma or space. Note: $name
expansion is not supported.


(default: no)

Always add (Resent-) From:, To:, Date: or Message-ID: headers
when not present. Postfix 2.6 and later add these headers only
when clients match the local_header_rewrite_clients parameter
setting. Earlier Postfix versions always add these headers; this
may break DKIM signatures that cover non-existent headers.
The undisclosed_recipients_header parameter setting determines
whether a To: header will be added.


(default: empty)

Optional address that receives a “blind carbon copy” of each message
that is received by the Postfix mail system.

Note: with Postfix 2.3 and later the BCC address is added as if it
was specified with NOTIFY=NONE. The sender will not be notified
when the BCC address is undeliverable, as long as all down-stream
software implements RFC 3461.

Note: with Postfix 2.2 and earlier the sender will be notified
when the BCC address is undeliverable.

Note: automatic BCC recipients are produced only for new mail.
To avoid mailer loops, automatic BCC recipients are not generated
after Postfix forwards mail internally, or after Postfix generates
mail itself.


(default: 60s)

The time unit over which client connection rates and other rates
are calculated.

This feature is implemented by the anvil(8) service which is available
in Postfix version 2.2 and later.

The default interval is relatively short. Because of the high
frequency of updates, the anvil(8) server uses volatile memory
only. Thus, information is lost whenever the process terminates.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 600s)

How frequently the anvil(8) connection and rate limiting server
logs peak usage information.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.2 and later.


(default: yes)

With locally submitted mail, append the string “@$myorigin” to mail
addresses without domain information. With remotely submitted mail,
append the string “@$remote_header_rewrite_domain” instead.

Note 1: this feature is enabled by default and must not be turned off.
Postfix does not support domain-less addresses.

Note 2: with Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true:

To get the behavior before Postfix version 2.2, specify
local_header_rewrite_clients = static:all”.


(default: Postfix ≥ 3.0: no, Postfix < 3.0: yes)

With locally submitted mail, append the string “.$mydomain” to
addresses that have no “.domain” information. With remotely submitted
mail, append the string “.$remote_header_rewrite_domain
instead.

Note 1: this feature is enabled by default. If disabled, users will not be
able to send mail to “user@partialdomainname” but will have to
specify full domain names instead.

Note 2: with Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true:

To get the behavior before Postfix version 2.2, specify
local_header_rewrite_clients = static:all”.


(default: 100s)

How long the postkick(1) command waits for a request to enter the
Postfix daemon process input buffer before giving up.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: static:anyone)

List of users who are authorized to flush the queue.

By default, all users are allowed to flush the queue. Access is
always granted if the invoking user is the super-user or the
$mail_owner user. Otherwise, the real UID of the process is looked
up in the system password file, and access is granted only if the
corresponding login name is on the access list. The username
“unknown” is used for processes whose real UID is not found in the
password file.

Specify a list of user names, “/file/name” or “type:table” patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A “/file/name”
pattern is replaced
by its contents; a “type:table” lookup table is matched when a name
matches a lookup key (the lookup result is ignored). Continue long
lines by starting the next line with whitespace. Specify “!pattern”
to exclude a name from the list. The form “!/file/name” is supported
only in Postfix version 2.4 and later.

This feature is available in Postfix 2.2 and later.


(default: static:anyone)

List of users who are authorized to view the queue.

By default, all users are allowed to view the queue. Access is
always granted if the invoking user is the super-user or the
$mail_owner user. Otherwise, the real UID of the process is looked
up in the system password file, and access is granted only if the
corresponding login name is on the access list. The username
“unknown” is used for processes whose real UID is not found in the
password file.

Specify a list of user names, “/file/name” or “type:table” patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A “/file/name”
pattern is replaced
by its contents; a “type:table” lookup table is matched when a name
matches a lookup key (the lookup result is ignored). Continue long
lines by starting the next line with whitespace. Specify “!pattern”
to exclude a user name from the list. The form “!/file/name” is
supported only in Postfix version 2.4 and later.

This feature is available in Postfix 2.2 and later.


(default: static:anyone)

List of users who are authorized to submit mail with the sendmail(1)
command (and with the privileged postdrop(1) helper command).

By default, all users are allowed to submit mail. Otherwise, the
real UID of the process is looked up in the system password file,
and access is granted only if the corresponding login name is on
the access list. The username “unknown” is used for processes
whose real UID is not found in the password file. To deny mail
submission access to all users specify an empty list.

Specify a list of user names, “/file/name” or “type:table” patterns,
separated by commas and/or whitespace. The list is matched left to right,
and the search stops on the first match. A “/file/name” pattern is
replaced by its contents;
a “type:table” lookup table is matched when a name matches a lookup key
(the lookup result is ignored). Continue long lines by starting the
next line with whitespace. Specify “!pattern” to exclude a user
name from the list. The form “!/file/name” is supported only in
Postfix version 2.4 and later.

Example:

authorized_submit_users = !www, static:all

This feature is available in Postfix 2.2 and later.


(default: $mynetworks)

What remote SMTP clients are allowed to specify the XVERP command.
This command requests that mail be delivered one recipient at a
time with a per recipient return address.

By default, only trusted clients are allowed to specify XVERP.

This parameter was introduced with Postfix version 1.1. Postfix
version 2.1 renamed this parameter to smtpd_authorized_verp_clients
and changed the default to none.

Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it), “/file/name” or “type:table” patterns. A “/file/name”
pattern is replaced by its contents; a “type:table” lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored). Continue long lines by starting the next line
with whitespace. Specify “!pattern” to exclude an address or network
block from the list. The form “!/file/name” is supported only in
Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside
[] in the authorized_verp_clients value, and in files
specified with “/file/name”. IP version 6 addresses contain the
“:” character, and would otherwise be confused with a “type:table
pattern.


(default: yes)

Produce additional bounce(8) logfile records that can be read by
Postfix versions before 2.0. The current and more extensible “name =
value” format is needed in order to implement more sophisticated
functionality.

This feature is available in Postfix 2.1 and later.


(default: 16777216)

The per-table I/O buffer size for programs that create Berkeley DB
hash or btree tables. Specify a byte count.

This feature is available in Postfix 2.0 and later.


(default: 131072)

The per-table I/O buffer size for programs that read Berkeley DB
hash or btree tables. Specify a byte count.

This feature is available in Postfix 2.0 and later.


(default: empty)

Where the Postfix SMTP client should deliver mail when it detects
a “mail loops back to myself” error condition. This happens when
the local MTA is the best SMTP mail exchanger for a destination
not listed in $mydestination, $inet_interfaces, $proxy_interfaces,
$virtual_alias_domains, or $virtual_mailbox_domains. By default,
the Postfix SMTP client returns such mail as undeliverable.

Specify, for example, “best_mx_transport = local” to pass the mail
from the Postfix SMTP client to the local(8) delivery agent. You
can specify
any message delivery “transport” or “transport:nexthop” that is
defined in the master.cf file. See the transport(5) manual page
for the syntax and meaning of “transport” or “transport:nexthop”.

However, this feature is expensive because it ties up a Postfix
SMTP client process while the local(8) delivery agent is doing its
work. It is more efficient (for Postfix) to list all hosted domains
in a table or database.


(default: yes)

Whether or not to use the local biff service. This service sends
“new mail” notifications to users who have requested new mail
notification with the UNIX command “biff y”.

For compatibility reasons this feature is on by default. On systems
with lots of interactive users, the biff service can be a performance
drain. Specify “biff = no” in main.cf to disable.


(default: empty)

Optional lookup tables for content inspection as specified in
the body_checks(5) manual page.

Note: with Postfix versions before 2.0, these rules inspect
all content after the primary message headers.


(default: 51200)

How much text in a message body segment (or attachment, if you
prefer to use that term) is subjected to body_checks inspection.
The amount of text is limited to avoid scanning huge attachments.

This feature is available in Postfix 2.0 and later.


(default: postmaster)

The recipient of postmaster notifications with the message headers
of mail that Postfix did not deliver and of SMTP conversation
transcripts of mail that Postfix did not receive. This feature is
enabled with the notify_classes parameter.


(default: 5d)

Consider a bounce message as undeliverable, when delivery fails
with a temporary error, and the time in the queue has reached the
bounce_queue_lifetime limit. By default, this limit is the same
as for regular mail.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

Specify 0 when mail delivery should be tried only once.

This feature is available in Postfix 2.1 and later.


(default: bounce)

The name of the bounce(8) service. This service maintains a record
of failed delivery attempts and generates non-delivery notifications.

This feature is available in Postfix 2.0 and later.


(default: 50000)

The maximal amount of original message text that is sent in a
non-delivery notification. Specify a byte count. A message is
returned as either message/rfc822 (the complete original) or as
text/rfc822-headers (the headers only). With Postfix version 2.4
and earlier, a message is always returned as message/rfc822 and is
truncated when it exceeds the size limit.

Notes:


(default: empty)

Pathname of a configuration file with bounce message templates.
These override the built-in templates of delivery status notification
(DSN) messages for undeliverable mail, delayed mail, successful
delivery, or delivery verification. The bounce(5) manual page
describes how to edit and test template files.

Template message body text may contain $name references to
Postfix configuration parameters. The result of $name expansion can
be previewed with “postconf -b file_name” before the file
is placed into the Postfix configuration directory.

This feature is available in Postfix 2.3 and later.


(default: no)

Enable interoperability with remote SMTP clients that implement an obsolete
version of the AUTH command (RFC 4954). Examples of such clients
are MicroSoft Outlook Express version 4 and MicroSoft Exchange
version 5.0.

Specify “broken_sasl_auth_clients = yes” to have Postfix advertise
AUTH support in a non-standard way.


(default: envelope_sender, envelope_recipient, header_sender, header_recipient)

What addresses are subject to canonical_maps address mapping.
By default, canonical_maps address mapping is applied to envelope
sender and recipient addresses, and to header sender and header
recipient addresses.

Specify one or more of: envelope_sender, envelope_recipient,
header_sender, header_recipient

This feature is available in Postfix 2.2 and later.


(default: empty)

Optional address mapping lookup tables for message headers and
envelopes. The mapping is applied to both sender and recipient
addresses, in both envelopes and in headers, as controlled
with the canonical_classes parameter. This is typically used
to clean up dirty addresses from legacy mail systems, or to replace
login names by Firstname.Lastname. The table format and lookups
are documented in canonical(5). For an overview of Postfix address
manipulations see the ADDRESS_REWRITING_README document.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.
Note: these lookups are recursive.

If you use this feature, run “postmap /etc/postfix/canonical” to
build the necessary DBM or DB file after every change. The changes
will become visible after a minute or so. Use “postfix reload
to eliminate the delay.

Note: with Postfix version 2.2, message header address mapping
happens only when message header address rewriting is enabled:

To get the behavior before Postfix version 2.2, specify
local_header_rewrite_clients = static:all”.

Examples:

canonical_maps = dbm:/etc/postfix/canonical
canonical_maps = hash:/etc/postfix/canonical

(default: cleanup)

The name of the cleanup(8) service. This service rewrites addresses
into the standard form, and performs canonical(5) address mapping
and virtual(5) aliasing.

This feature is available in Postfix 2.0 and later.


(default: see “postconf -d” output)

The location of all postfix administrative commands.


(default: empty)

The local(8) delivery agent working directory for delivery to
external commands. Failure to change directory causes the delivery
to be deferred.

The command_execution_directory value is not subject to Postfix
configuration parameter $name expansion. Instead, the following
$name expansions are done on command_execution_directory before the
directory is used. Expansion happens in the context
of the delivery request. The result of $name expansion is filtered
with the character set that is specified with the
execution_directory_expansion_filter parameter.

$user
The recipient’s username.
$shell
The recipient’s login shell pathname.
$home
The recipient’s home directory.
$recipient
The full recipient address.
$extension
The optional recipient address extension.
$domain
The recipient domain.
$local
The entire recipient localpart.
$recipient_delimiter
The address extension delimiter that was found in the recipient
address (Postfix 2.11 and later), or the system-wide recipient
address extension delimiter (Postfix 2.10 and earlier).
${name?value}
${name?{value}} (Postfix ≥ 3.0)
Expands to value when $name is non-empty.
${name:value}
${name:{value}} (Postfix ≥ 3.0)
Expands to value when $name is empty.
${name?{value1}:{value2}} (Postfix ≥ 3.0)
Expands to value1 when $name is non-empty,
value2 otherwise.

Instead of $name you can also specify ${name} or $(name).

This feature is available in Postfix 2.2 and later.


(default: see “postconf -d” output)

Restrict the characters that the local(8) delivery agent allows in
$name expansions of $mailbox_command and $command_execution_directory.
Characters outside the
allowed set are replaced by underscores.


(default: 1000s)

Time limit for delivery to external commands. This limit is used
by the local(8) delivery agent, and is the default time limit for
delivery by the pipe(8) delivery agent.

Note: if you set this time limit to a large value you must update the
global ipc_timeout parameter as well.


(default: 0)

A safety net that causes Postfix to run with backwards-compatible
default settings after an upgrade to a newer Postfix version.

With backwards compatibility turned on (the main.cfcompatibility_level
value is less than the Postfix built-in value), Postfix looks for
settings that are left at their implicit default value, and logs a
message when a backwards-compatible default setting is required.

using backwards-compatible default setting name=value
    to [accept a specific client request]

using backwards-compatible default setting name=value
    to [enable specific Postfix behavior]

See COMPATIBILITY_README for specific message details. If such
a message is logged in the context of a legitimate request, the
system administrator should make the backwards-compatible setting
permanent in main.cf or master.cf, for example:

# postconfname=value
# postfix reload

When no more backwards-compatible settings need to be made
permanent, the administrator should turn off backwards compatibility
by updating the compatibility_level setting in main.cf:

# postconf compatibility_level=N
# postfix reload

For N specify the number that is logged in your postfix(1)
warning message:

warning: To disable backwards compatibility use "postconf
    compatibility_level=N" and "postfix reload"

Starting with Postfix version 3.6, the compatibility level in
the above warning message is the Postfix version that introduced
the last incompatible change. The level is formatted as
major.minor.patch, where patch is usually omitted and
defaults to zero. Earlier compatibility levels are 0, 1 and 2.

NOTE: this also introduces support for the “<level”,
“<=level”, and other operators to compare compatibility levels.
With the standard operators “<“, “<=”, etc., compatibility
level “3.10” would be smaller than “3.9” which is undesirable.

This feature is available in Postfix 3.0 and later.


(default: see “postconf -d” output)

The default location of the Postfix main.cf and master.cf
configuration files. This can be overruled via the following
mechanisms:

  • The MAIL_CONFIG environment variable (daemon processes
    and commands).

  • The “-c” command-line option (commands only).

With Postfix commands that run with set-gid privileges, a
config_directory override either requires root privileges, or it
requires that the directory is listed with the alternate_config_directories
parameter in the default main.cf file.


(default: no)

After sending a “your message is delayed” notification, inform
the sender when the delay clears up. This can result in a sudden
burst of notifications at the end of a prolonged network outage,
and is therefore disabled by default.

See also: delay_warning_time.

This feature is available in Postfix 3.0 and later.


(default: 5s)

Time limit for connection cache connect, send or receive
operations. The time limit is enforced in the client.

This feature is available in Postfix 2.3 and later.


(default: scache)

The name of the scache(8) connection cache service. This service
maintains a limited pool of cached sessions.

This feature is available in Postfix 2.2 and later.


(default: 600s)

How frequently the scache(8) server logs usage statistics with
connection cache hit and miss rates for logical destinations and for
physical endpoints.


(default: 2s)

The maximal time-to-live value that the scache(8) connection
cache server
allows. Requests that specify a larger TTL will be stored with the
maximum allowed TTL. The purpose of this additional control is to
protect the infrastructure against careless people. The cache TTL
is already bounded by $max_idle.


(default: empty)

After the message is queued, send the entire message to the
specified transport:destination. The transport name
specifies the first field of a mail delivery agent definition in
master.cf; the syntax of the next-hop destination is described
in the manual page of the corresponding delivery agent. More
information about external content filters is in the Postfix
FILTER_README file.

Notes:


(default: empty)

Search path for Cyrus SASL application configuration files,
currently used only to locate the $smtpd_sasl_path.conf file.
Specify zero or more directories separated by a colon character,
or an empty value to use Cyrus SASL’s built-in search path.

This feature is available in Postfix 2.5 and later when compiled
with Cyrus SASL 2.1.22 or later.


(default: see “postconf -d” output)

The directory with Postfix support programs and daemon programs.
These should not be invoked directly by humans. The directory must
be owned by root.


(default: no)

How a Postfix daemon process handles errors while opening lookup
tables: gradual degradation or immediate termination.

no (default)

Gradual degradation: a
daemon process logs a message of type “error” and continues execution
with reduced functionality. Features that do not depend on the
unavailable table will work normally, while features that depend
on the table will result in a type “warning” message.
When
the notify_classes parameter value contains the “data” class, the
Postfix SMTP server and client will report transcripts of sessions
with an error because a table is unavailable.

yes (historical behavior)

Immediate
termination: a daemon process logs a type “fatal” message and
terminates immediately. This option reduces the number of possible
code paths through Postfix, and may therefore be slightly more
secure than the default.

For the sake of sanity, the number of type “error” messages is
limited to 13 over the lifetime of a daemon process.

This feature is available in Postfix 2.9 and later.


(default: 18000s)

How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: see “postconf -d” output)

The directory with Postfix-writable data files (for example:
caches, pseudo-random numbers). This directory must be owned by
the mail_owner account, and must not be shared with non-Postfix
software.

This feature is available in Postfix 2.5 and later.


(default: 2)

The increment in verbose logging level when a nexthop destination,
remote client or server name or network address matches a pattern
given with the debug_peer_list parameter.

Per-nexthop debug logging is available in Postfix 3.6 and later.


(default: empty)

Optional list of nexthop destination, remote client or server
name or network address patterns that, if matched, cause the verbose
logging level to increase by the amount specified in $debug_peer_level.

Per-nexthop debug logging is available in Postfix 3.6 and later.

Specify domain names, network/netmask patterns, “/file/name”
patterns or “type:table” lookup tables. The right-hand side result
from “type:table” lookups is ignored.

Pattern matching of domain names is controlled by the presence
or absence of “debug_peer_list” in the parent_domain_matches_subdomains
parameter value.

Examples:

debug_peer_list = 127.0.0.1
debug_peer_list = example.com

(default: empty)

The external command to execute when a Postfix daemon program is
invoked with the -D option.

Use “command .. & sleep 5” so that the debugger can attach before
the process marches on. If you use an X-based debugger, be sure to
set up your XAUTHORITY environment variable before starting Postfix.

Note: the command is subject to $name expansion, before it is
passed to the default command interpreter. Specify “$$” to
produce a single “$” character.

Example:

debugger_command =
    PATH=/usr/bin:/usr/X11R6/bin
    ddd $daemon_directory/$process_name $process_id & sleep 5

(default: see “postconf -d” output)

The default database type for use in newaliases(1), postalias(1)
and postmap(1) commands. On many UNIX systems the default type is
either dbm or hash. The default setting is frozen
when the Postfix system is built.

Examples:

default_database_type = hash
default_database_type = dbm

(default: 5)

How often the Postfix queue manager’s scheduler is allowed to
preempt delivery of one message with another.

Each transport maintains a so-called “available delivery slot counter”
for each message. One message can be preempted by another one when
the other message can be delivered using no more delivery slots
(i.e., invocations of delivery agents) than the current message
counter has accumulated (or will eventually accumulate – see about
slot loans below). This parameter controls how often the counter is
incremented – it happens after each default_delivery_slot_cost
recipients have been delivered.

The cost of 0 is used to disable the preempting scheduling completely.
The minimum value the scheduling algorithm can use is 2 – use it
if you want to maximize the message throughput rate. Although there
is no maximum, it doesn’t make much sense to use values above say
50.

The only reason why the value of 2 is not the default is the way
this parameter affects the delivery of mailing-list mail. In the
worst case, delivery can take somewhere between (cost 1/cost)
and (cost/cost-1) times more than if the preemptive scheduler was
disabled. The default value of 5 turns out to provide reasonable
message response times while making sure the mailing-list deliveries
are not extended by more than 20-25 percent even in the worst case.

Use transport_delivery_slot_cost to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.

Examples:

default_delivery_slot_cost = 0
default_delivery_slot_cost = 2

(default: 50)

The default value for transport-specific _delivery_slot_discount
settings.

This parameter speeds up the moment when a message preemption can
happen. Instead of waiting until the full amount of delivery slots
required is available, the preemption can happen when
transport_delivery_slot_discount percent of the required amount
plus transport_delivery_slot_loan still remains to be accumulated.
Note that the full amount will still have to be accumulated before
another preemption can take place later.

Use transport_delivery_slot_discount to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.


(default: 3)

The default value for transport-specific _delivery_slot_loan
settings.

This parameter speeds up the moment when a message preemption can
happen. Instead of waiting until the full amount of delivery slots
required is available, the preemption can happen when
transport_delivery_slot_discount percent of the required amount
plus transport_delivery_slot_loan still remains to be accumulated.
Note that the full amount will still have to be accumulated before
another preemption can take place later.

Use transport_delivery_slot_loan to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.


(default: empty)

Optional filter to replace the delivery status code or explanatory
text of successful or unsuccessful deliveries. This does not allow
the replacement of a successful status code (2.X.X) with an
unsuccessful status code (4.X.X or 5.X.X) or vice versa.

Note: the (smtp|lmtp)_delivery_status_filter is applied only
once per recipient: when delivery is successful, when delivery is
rejected with 5XX, or when there are no more alternate MX or A
destinations. Use smtp_reply_filter or lmtp_reply_filter to inspect
responses for all delivery attempts.

The following parameters can be used to implement a filter for
specific delivery agents: lmtp_delivery_status_filter,
local_delivery_status_filter, pipe_delivery_status_filter,
smtp_delivery_status_filter or virtual_delivery_status_filter. These
parameters support the same filter syntax as described here.

Specify zero or more “type:table” lookup table names, separated
by comma or whitespace. For each successful or unsuccessful delivery
to a recipient, the tables are queried in the specified order with
one line of text that is structured as follows:


enhanced-status-code SPACE explanatory-text

The first table match wins. The lookup result must have the
same structure as the query, a successful status code (2.X.X) must
be replaced with a successful status code, an unsuccessful status
code (4.X.X or 5.X.X) must be replaced with an unsuccessful status
code, and the explanatory text field must be non-empty. Other results
will result in a warning.

Example 1: convert specific soft TLS errors into hard errors,
by overriding the first number in the enhanced status code.

/etc/postfix/main.cf:
    smtp_delivery_status_filter = pcre:/etc/postfix/smtp_dsn_filter

/etc/postfix/smtp_dsn_filter:
    /^4(.d .d  TLS is required, but host S  refused to start TLS: . )/
        5$1
    /^4(.d .d  TLS is required, but was not offered by host . )/
        5$1
    # Do not change the following into hard bounces. They may
    # result from a local configuration problem.
    # 4.d .d  TLS is required, but our TLS engine is unavailable
    # 4.d .d  TLS is required, but unavailable
    # 4.d .d  Cannot start TLS: handshake failure

Example 2: censor the per-recipient delivery status text so
that it does not reveal the destination command or filename
when a remote sender requests confirmation of successful delivery.

/etc/postfix/main.cf:
    local_delivery_status_filter = pcre:/etc/postfix/local_dsn_filter

/etc/postfix/local_dsn_filter:
    /^(2S  delivered to file). /    $1
    /^(2S  delivered to command). / $1

Notes:

This feature is available in Postfix 3.0 and later.


(default: 1)

How many pseudo-cohorts must suffer connection or handshake
failure before a specific destination is considered unavailable
(and further delivery is suspended). Specify zero to disable this
feature. A destination’s pseudo-cohort failure count is reset each
time a delivery completes without connection or handshake failure
for that specific destination.

A pseudo-cohort is the number of deliveries equal to a destination’s
delivery concurrency.

Use transport_destination_concurrency_failed_cohort_limit to specify
a transport-specific override, where transport is the master.cf
name of the message delivery transport.

This feature is available in Postfix 2.5. The default setting
is compatible with earlier Postfix versions.


(default: 20)

The default maximal number of parallel deliveries to the same
destination. This is the default limit for delivery via the lmtp(8),
pipe(8), smtp(8) and virtual(8) delivery agents.
With a per-destination recipient limit > 1, a destination is a domain,
otherwise it is a recipient.

Use transport_destination_concurrency_limit to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.


(default: 1)

The per-destination amount of delivery concurrency negative
feedback, after a delivery completes with a connection or handshake
failure. Feedback values are in the range 0..1 inclusive. With
negative feedback, concurrency is decremented at the beginning of
a sequence of length 1/feedback. This is unlike positive feedback,
where concurrency is incremented at the end of a sequence of length
1/feedback.

As of Postfix version 2.5, negative feedback cannot reduce
delivery concurrency to zero. Instead, a destination is marked
dead (further delivery suspended) after the failed pseudo-cohort
count reaches $default_destination_concurrency_failed_cohort_limit
(or $transport_destination_concurrency_failed_cohort_limit).
To make the scheduler completely immune to connection or handshake
failures, specify a zero feedback value and a zero failed pseudo-cohort
limit.

Specify one of the following forms:

number
number / number
Constant feedback. The value must be in the range 0..1 inclusive.
The default setting of “1” is compatible with Postfix versions
before 2.5, where a destination’s delivery concurrency is throttled
down to zero (and further delivery suspended) after a single failed
pseudo-cohort.
number / concurrency
Variable feedback of “number / (delivery concurrency)”.
The number must be in the range 0..1 inclusive. With
number equal to “1”, a destination’s delivery concurrency
is decremented by 1 after each failed pseudo-cohort.

A pseudo-cohort is the number of deliveries equal to a destination’s
delivery concurrency.

Use transport_destination_concurrency_negative_feedback
to specify a transport-specific override, where transport
is the master.cf
name of the message delivery transport.

This feature is available in Postfix 2.5. The default setting
is compatible with earlier Postfix versions.


(default: 1)

The per-destination amount of delivery concurrency positive
feedback, after a delivery completes without connection or handshake
failure. Feedback values are in the range 0..1 inclusive. The
concurrency increases until it reaches the per-destination maximal
concurrency limit. With positive feedback, concurrency is incremented
at the end of a sequence with length 1/feedback. This is unlike
negative feedback, where concurrency is decremented at the start
of a sequence of length 1/feedback.

Specify one of the following forms:

number
number / number
Constant feedback. The value must be in the range 0..1
inclusive. The default setting of “1” is compatible with Postfix
versions before 2.5, where a destination’s delivery concurrency
doubles after each successful pseudo-cohort.
number / concurrency
Variable feedback of “number / (delivery concurrency)”.
The number must be in the range 0..1 inclusive. With
number equal to “1”, a destination’s delivery concurrency
is incremented by 1 after each successful pseudo-cohort.

A pseudo-cohort is the number of deliveries equal to a destination’s
delivery concurrency.

Use transport_destination_concurrency_positive_feedback
to specify a transport-specific override, where transport
is the master.cf name of the message delivery transport.

This feature is available in Postfix 2.5 and later.


(default: 0s)

The default amount of delay that is inserted between individual
message deliveries to the same destination and over the same message
delivery transport. Specify a non-zero value to rate-limit those
message deliveries to at most one per $default_destination_rate_delay.

The resulting behavior depends on the value of the corresponding
per-destination recipient limit.

To enable the delay, specify a non-zero time value (an integral
value plus an optional one-letter suffix that specifies the time
unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). The default time unit is s (seconds).

NOTE: the delay is enforced by the queue manager. The delay
timer state does not survive “postfix reload” or “postfix
stop
“.

Use transport_destination_rate_delay to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.

NOTE: with a non-zero _destination_rate_delay, specify a
transport_destination_concurrency_failed_cohort_limit of 10
or more to prevent Postfix from deferring all mail for the same
destination after only one connection or handshake error.

This feature is available in Postfix 2.5 and later.


(default: 50)

The default maximal number of recipients per message delivery.
This is the default limit for delivery via the lmtp(8), pipe(8),
smtp(8) and virtual(8) delivery agents.

Setting this parameter to a value of 1 affects email deliveries
as follows:

Use transport_destination_recipient_limit to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.


(default: 1000)

The default value for the extra per-transport limit imposed on the
number of in-memory recipients. This extra recipient space is
reserved for the cases when the Postfix queue manager’s scheduler
preempts one message with another and suddenly needs some extra
recipient slots for the chosen message in order to avoid performance
degradation.

Use transport_extra_recipient_limit to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.


(default: empty)

When a content_filter or FILTER request specifies no explicit
next-hop destination, use $default_filter_nexthop instead; when
that value is empty, use the domain in the recipient address.
Specify “default_filter_nexthop = $myhostname” for compatibility
with Postfix version 2.6 and earlier, or specify an explicit next-hop
destination with each content_filter value or FILTER action.

This feature is available in Postfix 2.7 and later.


(default: 3)

How many recipients a message must have in order to invoke the
Postfix queue manager’s scheduling algorithm at all. Messages
which would never accumulate at least this many delivery slots
(subject to slot cost parameter as well) are never preempted.

Use transport_minimum_delivery_slots to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.


(default: nobody)

The default rights used by the local(8) delivery agent for delivery
to an external file or command. These rights are used when delivery
is requested from an aliases(5) file that is owned by root, or
when delivery is done on behalf of root. DO NOT SPECIFY A
PRIVILEGED USER OR THE POSTFIX OWNER
.


(default: 100)

The default maximal number of Postfix child processes that provide
a given service. This limit can be overruled for specific services
in the master.cf file.


(default: see “postconf -d” output)

The default Postfix SMTP server response template for a request that is
rejected by an RBL-based restriction. This template can be overruled
by specific entries in the optional rbl_reply_maps lookup table.

This feature is available in Postfix 2.0 and later.

The template does not support Postfix configuration parameter $name
substitution. Instead, it supports exactly one level of $name
substitution for the following attributes:

$client
The client hostname and IP address, formatted as name[address].
$client_address
The client IP address.
$client_name
The client hostname or “unknown”. See reject_unknown_client_hostname
for more details.
$reverse_client_name
The client hostname from address->name lookup, or “unknown”.
See reject_unknown_reverse_client_hostname for more details.
$helo_name
The hostname given in HELO or EHLO command or empty string.
$rbl_class
The denylisted entity type: Client host, Helo command, Sender
address, or Recipient address.
$rbl_code
The numerical SMTP response code, as specified with the
maps_rbl_reject_code configuration parameter. Note: The numerical
SMTP response code is required, and must appear at the start of the
reply. With Postfix version 2.3 and later this information may be followed
by an RFC 3463 enhanced status code.
$rbl_domain
The RBL domain where $rbl_what is denylisted.
$rbl_reason
The reason why $rbl_what is denylisted, or an empty string.
$rbl_what
The entity that is denylisted (an IP address, a hostname, a domain
name, or an email address whose domain was denylisted).
$recipient
The recipient address or <> in case of the null address.
$recipient_domain
The recipient domain or empty string.
$recipient_name
The recipient address localpart or <> in case of null address.
$sender
The sender address or <> in case of the null address.
$sender_domain
The sender domain or empty string.
$sender_name
The sender address localpart or <> in case of the null address.
${name?value}
${name?{value}} (Postfix ≥ 3.0)
Expands to value when $name is non-empty.
${name:value}
${name:{value}} (Postfix ≥ 3.0)
Expands to value when $name is empty.
${name?{value1}:{value2}} (Postfix ≥ 3.0)
Expands to value1 when $name is non-empty,
value2 otherwise.

Instead of $name you can also specify ${name} or $(name).

Note: when an enhanced status code is specified in an RBL reply
template, it is subject to modification. The following transformations
are needed when the same RBL reply template is used for client,
helo, sender, or recipient access restrictions.

  • When rejecting a sender address, the Postfix SMTP server
    will transform a recipient DSN status (e.g., 4.1.1-4.1.6) into the
    corresponding sender DSN status, and vice versa.

  • When rejecting non-address information (such as the HELO
    command argument or the client hostname/address), the Postfix SMTP
    server will transform a sender or recipient DSN status into a generic
    non-address DSN status (e.g., 4.0.0).


(default: 20000)

The default per-transport upper limit on the number of in-memory
recipients. These limits take priority over the global
qmgr_message_recipient_limit after the message has been assigned
to the respective transports. See also default_extra_recipient_limit
and qmgr_message_recipient_minimum.

Use transport_recipient_limit to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.


(default: 5s)

The default per-transport maximum delay between refilling recipients.
When not all message recipients fit into memory at once, keep loading
more of them at least once every this many seconds. This is used to
make sure the recipients are refilled in a timely manner even when
$default_recipient_refill_limit is too high for too slow deliveries.

Use transport_recipient_refill_delay to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.

This feature is available in Postfix 2.4 and later.


(default: 100)

The default per-transport limit on the number of recipients refilled at
once. When not all message recipients fit into memory at once, keep
loading more of them in batches of at least this many at a time. See also
$default_recipient_refill_delay, which may result in recipient batches
lower than this when this limit is too high for too slow deliveries.

Use transport_recipient_refill_limit to specify a
transport-specific override, where transport is the master.cf
name of the message delivery transport.

This feature is available in Postfix 2.4 and later.


(default: smtp)

The default mail delivery transport and next-hop destination for
destinations that do not match $mydestination, $inet_interfaces,
$proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains,
or $relay_domains. This information can be overruled with the
sender_dependent_default_transport_maps parameter and with the
transport(5) table.

In order of decreasing precedence, the nexthop destination is taken
from $sender_dependent_default_transport_maps, $default_transport,
$sender_dependent_relayhost_maps, $relayhost, or from the recipient
domain.

Specify a string of the form transport:nexthop, where transport
is the name of a mail delivery transport defined in master.cf.
The :nexthop destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent. In the case of
SMTP or LMTP, specify one or more destinations separated by comma or
whitespace (with Postfix 3.5 and later).

Example:

default_transport = uucp:relayhostname

(default: 0s)

The default amount of delay that is inserted between individual
message deliveries over the same message delivery transport,
regardless of destination. Specify a non-zero value to rate-limit
those message deliveries to at most one per $default_transport_rate_delay.

Use transport_transport_rate_delay to specify a
transport-specific override, where the initial transport is
the master.cf name of the message delivery transport.

Example: throttle outbound SMTP mail to at most 3 deliveries
per minute.

/etc/postfix/main.cf:
    smtp_transport_rate_delay = 20s

To enable the delay, specify a non-zero time value (an integral
value plus an optional one-letter suffix that specifies the time
unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). The default time unit is s (seconds).

NOTE: the delay is enforced by the queue manager.

This feature is available in Postfix 3.1 and later.


(default: =)

The two default VERP delimiter characters. These are used when
no explicit delimiters are specified with the SMTP XVERP command
or with the “sendmail -XV” command-line option (Postfix 2.2
and earlier: -V). Specify characters that are allowed by the
verp_delimiter_filter setting.

This feature is available in Postfix 1.1 and later.


(default: 450)

The numerical Postfix SMTP server response code when a remote SMTP
client request is rejected by the “defer” restriction.

Do not change this unless you have a complete understanding of RFC 5321.


(default: defer)

The name of the defer service. This service is implemented by the
bounce(8) daemon and maintains a record
of failed delivery attempts and generates non-delivery notifications.

This feature is available in Postfix 2.0 and later.


(default: empty)

The names of message delivery transports that should not deliver mail
unless someone issues “sendmail -q” or equivalent. Specify zero
or more mail delivery transport names that appear in the
first field of master.cf.

Example:

defer_transports = smtp

(default: 2)

The maximal number of digits after the decimal point when logging
sub-second delay values. Specify a number in the range 0..6.

Large delay values are rounded off to an integral number of seconds;
delay values below the delay_logging_resolution_limit are logged
as “0”, and delay values under 100s are logged with at most two-digit
precision.

The format of the “delays=a/b/c/d” logging is as follows:

This feature is available in Postfix 2.3 and later.


(default: postmaster)

The recipient of postmaster notifications with the message headers
of mail that cannot be delivered within $delay_warning_time time
units.

See also: delay_warning_time, notify_classes.


(default: 0h)

The time after which the sender receives a copy of the message
headers of mail that is still queued. The confirm_delay_cleared
parameter controls sender notification when the delay clears up.

To enable this feature, specify a non-zero time value (an integral
value plus an optional one-letter suffix that specifies the time
unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).

See also: delay_notice_recipient, notify_classes, confirm_delay_cleared.


(default: 20)

The maximal number of attempts to acquire an exclusive lock on a
mailbox file or bounce(8) logfile.


(default: 1s)

The time between attempts to acquire an exclusive lock on a mailbox
file or bounce(8) logfile.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: no)

Make the queue manager’s feedback algorithm verbose for performance
analysis purposes.

This feature is available in Postfix 2.5 and later.


(default: yes)

Automatically detect 8BITMIME body content by looking at
Content-Transfer-Encoding: message headers; historically, this
behavior was hard-coded to be “always on”.

This feature is available in Postfix 2.5 and later.


(default: no)

Disable DNS lookups in the Postfix SMTP and LMTP clients. When
disabled, hosts are looked up with the getaddrinfo() system
library routine which normally also looks in /etc/hosts. As of
Postfix 2.11, this parameter is deprecated; use smtp_dns_support_level
instead.

DNS lookups are enabled by default.


(default: no)

Turn off MIME processing while receiving mail. This means that no
special treatment is given to Content-Type: message headers, and
that all text after the initial message headers is considered to
be part of the message body.

This feature is available in Postfix 2.0 and later.

Mime input processing is enabled by default, and is needed in order
to recognize MIME headers in message content.


(default: no)

Disable the conversion of 8BITMIME format to 7BIT format. Mime
output conversion is needed when the destination does not advertise
8BITMIME support.

This feature is available in Postfix 2.0 and later.


(default: no)

Disable sending one bounce report per recipient.

The default, one per recipient, is what ezmlm needs.

This feature is available in Postfix 1.1 and later.


(default: no)

Disable the SMTP VRFY command. This stops some techniques used to
harvest email addresses.

Example:

disable_vrfy_command = no

(default: no)

Enable a workaround for future libc incompatibility. The Postfix
implementation of RFC 2308 negative reply caching relies on the
promise that res_query() and res_search() invoke res_send(), which
returns the server response in an application buffer even if the
requested record does not exist. If this promise is broken, specify
“yes” to enable a workaround for DNS reputation lookups.

This feature is available in Postfix 3.1 and later.


(default: 0s)

A debugging aid to artificially delay DNS responses.

This feature is available in Postfix 2.8.


(default: dnsblog)

The name of the dnsblog(8) service entry in master.cf. This
service performs DNS allow/denylist lookups.

This feature is available in Postfix 2.8 and later.


(default: ns:.)

The DNS query type (default: “ns”) and DNS query name (default:
“.”) that Postfix may use to determine whether DNSSEC validation
is available.

Background: DNSSEC validation is needed for Postfix DANE support;
this ensures that Postfix receives TLSA records with secure TLS
server certificate info. When DNSSEC validation is unavailable,
mail deliveries using opportunistic DANE will not be protected
by server certificate info in TLSA records, and mail deliveries
using mandatory DANE will not be made at all.

By default, a Postfix process will send a DNSSEC probe after
1) the process made a DNS query that requested DNSSEC validation,
2) the process did not receive a DNSSEC validated response to this
query or to an earlier query, and 3) the process did not already
send a DNSSEC probe.

When the DNSSEC probe has no response, or when the response is
not DNSSEC validated, Postfix logs a warning that DNSSEC validation
may be unavailable.

Example:

warning: DNSSEC validation may be unavailable
warning: reason: dnssec_probe 'ns:.' received a response that is not DNSSEC validated
warning: reason: dnssec_probe 'ns:.' received no response: Server failure

Possible reasons why DNSSEC validation may be unavailable:

By default, the DNSSEC probe asks for the DNS root zone NS
records, because resolvers should always have that information
cached. If Postfix runs on a network where the DNS root zone is not
reachable, specify a different probe, or specify an empty dnssec_probe
value to disable the feature.

This feature is available in Postfix 3.6 and later. It was backported
to Postfix versions 3.5.9, 3.4.19, 3.3.16. 3.2.21.


(default: 0)

Don’t remove queue files and save them to the “saved” mail queue.
This is a debugging aid. To inspect the envelope information and
content of a Postfix queue file, use the postcat(1) command.


(default: double-bounce)

The sender address of postmaster notifications that are generated
by the mail system. All mail to this address is silently discarded,
in order to terminate mail bounce loops.


(default: 1000)

The maximal number of addresses remembered by the address
duplicate filter for aliases(5) or virtual(5) alias expansion, or
for showq(8) queue displays.


(default: <>)

The sender_dependent_default_transport_maps search string that
will be used instead of the null sender address.

This feature is available in Postfix 2.7 and later.


(default: <>)

The lookup key to be used in local_login_sender_maps tables, instead
of the null sender address.

This feature is available in Postfix 3.6 and later.


(default: MAILER-DAEMON)

The recipient of mail addressed to the null address. Postfix does
not accept such addresses in SMTP commands, but they may still be
created locally as the result of configuration or software error.


(default: <>)

The sender_dependent_relayhost_maps search string that will be
used instead of the null sender address.

This feature is available in Postfix 2.5 and later. With
earlier versions, sender_dependent_relayhost_maps lookups were
skipped for the null sender address.


(default: no)

Report mail delivery errors to the address specified with the
non-standard Errors-To: message header, instead of the envelope
sender address (this feature is removed with Postfix version 2.2, is
turned off by default with Postfix version 2.1, and is always turned on
with older Postfix versions).


(default: no)

Enable ‘transitional’ compatibility between IDNA2003 and IDNA2008,
when converting UTF-8 domain names to/from the ASCII form that is
used for DNS lookups. Specify “yes” for compatibility with Postfix
≤ 3.1 (not recommended). This affects the conversion of domain
names that contain for example the German sz and the Greek zeta.
See http://unicode.org/cldr/utility/idna.jsp for more examples.

This feature is available in Postfix 3.2 and later.


(default: no)

Enable long, non-repeating, queue IDs (queue file names). The
benefit of non-repeating names is simpler logfile analysis and
easier queue migration (there is no need to run “postsuper” to
change queue file names that don’t match their message file inode
number).

Note: see below for how to convert long queue file names to
Postfix ≤ 2.8.

Changing the parameter value to “yes” has the following effects:

Changing the parameter value to “no” has the following effects:

Before migration to Postfix ≤ 2.8, the following commands
are required to convert long queue file names into short names:

# postfix stop
# postconf enable_long_queue_ids=no
# postsuper

Repeat the postsuper command until it reports no more queue file
name changes.

This feature is available in Postfix 2.9 and later.


(default: yes)

Enable support for the original recipient address after an
address is rewritten to a different address (for example with
aliasing or with canonical mapping).

The original recipient address is used as follows:

Final delivery
With “enable_original_recipient =
yes”, the original recipient address is stored in the X-Original-To
message header. This header may be used to distinguish between
different recipients that share the same mailbox.
Recipient deduplication
With “enable_original_recipient
= yes”, the cleanup(8) daemon performs duplicate recipient elimination
based on the content of (original recipient, maybe-rewritten
recipient) pairs. Otherwise, the cleanup(8) daemon performs duplicate
recipient elimination based only on the maybe-rewritten recipient
address.

Note: with Postfix ≤ 3.2 the “setting enable_original_recipient
= no” breaks address verification for addresses that are
aliased or otherwise rewritten (Postfix is unable to store the
address verification result under the original probe destination
address; instead, it can store the result only under the rewritten
address).

This feature is available in Postfix 2.1 and later. Postfix
version 2.0 behaves as if this parameter is always set to yes.
Postfix versions before 2.0 have no support for the original recipient
address.


(default: no)

Enable non-delivery, success, and delay notifications that link
to the original message by including a References: and In-Reply-To:
header with the original Message-ID value. There are advantages and
disadvantages to consider.

advantage
This allows mail readers to present
a delivery status notification in the same email thread as the original
message.
disadvantage
This makes it easy for users to
mistakenly delete the whole email thread (all related messages),
instead of deleting only the non-delivery notification.

This feature is available in Postfix 3.6 and later.


(default: postmaster)

The recipient of postmaster notifications about mail delivery
problems that are caused by policy, resource, software or protocol
errors. These notifications are enabled with the notify_classes
parameter.


(default: error)

The name of the error(8) pseudo delivery agent. This service always
returns mail as undeliverable.

This feature is available in Postfix 2.0 and later.


(default: see “postconf -d” output)

Restrict the characters that the local(8) delivery agent allows
in $name expansions of $command_execution_directory. Characters
outside the allowed set are replaced by underscores.

This feature is available in Postfix 2.2 and later.


(default: no)

When delivering to an alias “aliasname” that has an
“owner-aliasname” companion alias, set the envelope sender
address to the expansion of the “owner-aliasname” alias.
Normally, Postfix sets the envelope sender address to the name of
the “owner-aliasname” alias.


(default: see “postconf -d” output)

The list of environment variables that a Postfix process will export
to non-Postfix processes. The TZ variable is needed for sane
time keeping on System-V-ish systems.

Specify a list of names and/or name=value pairs, separated by
whitespace or comma. Specify “{ name=value }” to protect whitespace
or comma in parameter values (whitespace after the opening “{” and
before the closing “}”
is ignored). The form name=value is supported with Postfix version
2.1 and later; the use of {} is supported with Postfix 3.0 and
later.

Example:

export_environment = TZ PATH=/bin:/usr/bin

(default: 10240)

The maximal number of recipient addresses that Postfix will extract
from message headers when mail is submitted with “sendmail -t“.

This feature was removed in Postfix version 2.1.


(default: empty)

Optional list of relay hosts for SMTP destinations that can’t be
found or that are unreachable. With Postfix 2.3 this parameter
is renamed to smtp_fallback_relay.

By default, mail is returned to the sender when a destination is
not found, and delivery is deferred when a destination is unreachable.

The fallback relays must be SMTP destinations. Specify a domain,
host, host:port, [host]:port, [address] or [address]:port; the form
[host] turns off MX lookups. If you specify multiple SMTP
destinations, Postfix will try them in the specified order.

Note: before Postfix 2.2, do not use the fallback_relay feature
when relaying mail
for a backup or primary MX domain. Mail would loop between the
Postfix MX host and the fallback_relay host when the final destination
is unavailable.

Postfix version 2.2 and later will not use the fallback_relay feature
for destinations that it is MX host for.


(default: empty)

Optional message delivery transport that the local(8) delivery
agent should use for names that are not found in the aliases(5)
or UNIX password database.

The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.


(default: empty)

Optional lookup tables with per-recipient message delivery
transports for recipients that the local(8) delivery agent could
not find in the aliases(5) or UNIX password database.

The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.

For safety reasons, this feature does not allow $number
substitutions in regular expression maps.

This feature is available in Postfix 2.3 and later.


(default: $relay_domains)

Optional list of destinations that are eligible for per-destination
logfiles with mail that is queued to those destinations.

By default, Postfix maintains “fast flush” logfiles only for
destinations that the Postfix SMTP server is willing to relay to
(i.e. the default is: “fast_flush_domains = $relay_domains“; see
the relay_domains parameter in the postconf(5) manual).

Specify a list of hosts or domains, “/file/name” patterns or
type:table” lookup tables, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace. A
“/file/name” pattern is replaced by its contents; a “type:table
lookup table is matched when the domain or its parent domain appears
as lookup key.

Pattern matching of domain names is controlled by the presence
or absence of “fast_flush_domains” in the parent_domain_matches_subdomains
parameter value.

Specify “fast_flush_domains =” (i.e., empty) to disable the feature
altogether.


(default: 7d)

The time after which an empty per-destination “fast flush” logfile
is deleted.

You can specify the time as a number, or as a number followed by
a letter that indicates the time unit: s=seconds, m=minutes, h=hours,
d=days, w=weeks. The default time unit is days.


(default: 12h)

The time after which a non-empty but unread per-destination “fast
flush” logfile needs to be refreshed. The contents of a logfile
are refreshed by requesting delivery of all messages listed in the
logfile.

You can specify the time as a number, or as a number followed by
a letter that indicates the time unit: s=seconds, m=minutes, h=hours,
d=days, w=weeks. The default time unit is hours.


(default: 0)

Force specific internal tests to fail, to test the handling of
errors that are difficult to reproduce otherwise.


(default: flush)

The name of the flush(8) service. This service maintains per-destination
logfiles with the queue file names of mail that is queued for those
destinations.

This feature is available in Postfix 2.0 and later.


(default: 5)

The maximal number of attempts to fork() a child process.


(default: 1s)

The delay between attempts to fork() a child process.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: see “postconf -d” output)

Restrict the characters that the local(8) delivery agent allows in
$name expansions of $forward_path. Characters outside the
allowed set are replaced by underscores.


(default: see “postconf -d” output)

The local(8) delivery agent search list for finding a .forward
file with user-specified delivery methods. The first file that is
found is used.

The forward_path value is not subject to Postfix configuration
parameter $name expansion. Instead, the following $name expansions
are done on forward_path before the search actually happens.
The result of $name expansion is
filtered with the character set that is specified with the
forward_expansion_filter parameter.

$user
The recipient’s username.
$shell
The recipient’s login shell pathname.
$home
The recipient’s home directory.
$recipient
The full recipient address.
$extension
The optional recipient address extension.
$domain
The recipient domain.
$local
The entire recipient localpart.
$recipient_delimiter
The address extension delimiter that was found in the recipient
address (Postfix 2.11 and later), or the system-wide recipient
address extension delimiter (Postfix 2.10 and earlier).
${name?value}
${name?{value}} (Postfix ≥ 3.0)
Expands to value when $name is non-empty.
${name:value}
${name:{value}} (Postfix ≥ 3.0)
Expands to value when $name is empty.
${name?{value1}:{value2}} (Postfix ≥ 3.0)
Expands to value1 when $name is non-empty,
value2 otherwise.

Instead of $name you can also specify ${name} or $(name).

Examples:

forward_path = /var/forward/$user
forward_path =
    /var/forward/$user/.forward$recipient_delimiter$extension,
    /var/forward/$user/.forward

(default: yes)

Update the local(8) delivery agent’s idea of the Delivered-To:
address (see prepend_delivered_header) only once, at the start of
a delivery attempt; do not update the Delivered-To: address while
expanding aliases or .forward files.

This feature is available in Postfix 2.3 and later. With older
Postfix releases, the behavior is as if this parameter is set to
“no”. The old setting can be expensive with deeply nested aliases
or .forward files. When an alias or .forward file changes the
Delivered-To: address, it ties up one queue file and one cleanup
process instance while mail is being forwarded.


(default: 1)

The number of subdirectory levels for queue directories listed with
the hash_queue_names parameter. Queue hashing is implemented by
creating one or more levels of directories with one-character names.
Originally, these directory names were equal to the first characters
of the queue file name, with the hexadecimal representation of the
file creation time in microseconds.

With long queue file names, queue hashing produces the same
results as with short names. The file creation time in microseconds
is converted into hexadecimal form before the result is used for
queue hashing. The base 16 encoding gives finer control over the
number of subdirectories than is possible with the base 52 encoding
of long queue file names.

After changing the hash_queue_names or hash_queue_depth parameter,
execute the command “postfix reload“.


(default: deferred, defer)

The names of queue directories that are split across multiple
subdirectory levels.

Before Postfix version 2.2, the default list of hashed queues
was significantly larger. Claims about improvements in file system
technology suggest that hashing of the incoming and active queues
is no longer needed. Fewer hashed directories speed up the time
needed to restart Postfix.

After changing the hash_queue_names or hash_queue_depth parameter,
execute the command “postfix reload“.


(default: 10240)

The maximal number of address tokens are allowed in an address
message header. Information that exceeds the limit is discarded.
The limit is enforced by the cleanup(8) server.


(default: empty)

Optional lookup tables for content inspection of primary non-MIME
message headers, as specified in the header_checks(5) manual page.


(default: standard)

The format of the Postfix-generated From: header. This
setting affects the appearance of ‘full name’ information when a
local program such as /bin/mail submits a message without a From:
header through the Postfix sendmail(1) command.

Specify one of the following:

standard (default)
Produce a header formatted
as “From:name <address>“.
This is the default as of Postfix 3.3.
obsolete
Produce a header formatted as “From:address(name)“. This is the behavior
prior to Postfix 3.3.

Notes:

This feature is available in Postfix 3.3 and later.


(default: 102400)

The maximal amount of memory in bytes for storing a message header.
If a header is larger, the excess is discarded. The limit is
enforced by the cleanup(8) server.


(default: yes)

Log warnings about problematic configuration settings, and provide
helpful suggestions.

This feature is available in Postfix 2.0 and later.


(default: empty)

Optional pathname of a mailbox file relative to a local(8) user’s
home directory.

Specify a pathname ending in “/” for qmail-style delivery.

The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.

Examples:

home_mailbox = Mailbox
home_mailbox = Maildir/

(default: 50)

The maximal number of Received: message headers that is allowed
in the primary message headers. A message that exceeds the limit
is bounced, in order to stop a mailer loop.


(default: see “postconf -d” output)

The location of Postfix HTML files that describe how to build,
configure or operate a specific Postfix subsystem or feature.


(default: no)

Ignore DNS MX lookups that produce no response. By default,
the Postfix SMTP client defers delivery and tries again after some
delay. This behavior is required by the SMTP standard.

Specify “ignore_mx_lookup_error = yes” to force a DNS A record
lookup instead. This violates the SMTP standard and can result in
mis-delivery of mail.


(default: see “postconf -d” output)

The list of environment variables that a privileged Postfix
process will import from a non-Postfix parent process, or name=value
environment overrides. Unprivileged utilities will enforce the
name=value overrides, but otherwise will not change their process
environment. Examples of relevant environment variables:

TZ
May be needed for sane time keeping on most System-V-ish systems.
DISPLAY
Needed for debugging Postfix daemons with an X-windows debugger.
XAUTHORITY
Needed for debugging Postfix daemons with an X-windows debugger.
MAIL_CONFIG
Needed to make “postfix -c” work.
POSTLOG_SERVICE
Needed to make “maillog_file” work during daemon
process initialization.
POSTLOG_HOSTNAME
Needed to make “maillog_file” work during daemon
process initialization.

Specify a list of names and/or name=value pairs, separated by
whitespace or comma. Specify “{ name=value }” to protect whitespace
or comma in environment variable values (whitespace after the opening “{” and
before the closing “}”
is ignored). The form name=value is supported with Postfix version
2.1 and later; the use of {} is supported with Postfix 3.0 and
later.


(default: 1s)

Time to pause before accepting a new message, when the message
arrival rate exceeds the message delivery rate. This feature is
turned on by default (it’s disabled on SCO UNIX due to an SCO bug).

With the default 100 Postfix SMTP server process limit, “in_flow_delay
= 1s” limits the mail inflow to 100 messages per second above the
number of messages delivered per second.

Specify 0 to disable the feature. Valid delays are 0..10.


(default: all)

The local network interface addresses that this mail system receives
mail on. Specify “all” to receive mail on all network
interfaces (default), and “loopback-only” to receive mail
on loopback network interfaces only (Postfix version 2.2 and later). The
parameter also controls delivery of mail to user@[ip.address].

Note 1: you need to stop and start Postfix when this parameter changes.

Note 2: address information may be enclosed inside [],
but this form is not required here.

When inet_interfaces specifies just one IPv4 and/or IPv6 address
that is not a loopback address, the Postfix SMTP client will use
this address as the IP source address for outbound mail. Support
for IPv6 is available in Postfix version 2.2 and later.

On a multi-homed firewall with separate Postfix instances listening on the
“inside” and “outside” interfaces, this can prevent each instance from
being able to reach remote SMTP servers on the “other side” of the
firewall. Setting
smtp_bind_address to 0.0.0.0 avoids the potential problem for
IPv4, and setting smtp_bind_address6 to :: solves the problem
for IPv6.

A better solution for multi-homed firewalls is to leave inet_interfaces
at the default value and instead use explicit IP addresses in
the master.cf SMTP server definitions. This preserves the Postfix
SMTP client’s
loop detection, by ensuring that each side of the firewall knows that the
other IP address is still the same host. Setting $inet_interfaces to a
single IPv4 and/or IPV6 address is primarily useful with virtual
hosting of domains on
secondary IP addresses, when each IP address serves a different domain
(and has a different $myhostname setting).

See also the proxy_interfaces parameter, for network addresses that
are forwarded to Postfix by way of a proxy or address translator.

Examples:

inet_interfaces = all (DEFAULT)
inet_interfaces = loopback-only (Postfix version 2.2 and later)
inet_interfaces = 127.0.0.1
inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
inet_interfaces = 192.168.1.2, 127.0.0.1

(default: see ‘postconf -d output’)

The Internet protocols Postfix will attempt to use when making
or accepting connections. Specify one or more of “ipv4”
or “ipv6”, separated by whitespace or commas. The form
“all” is equivalent to “ipv4, ipv6” or “ipv4”, depending
on whether the operating system implements IPv6.

With Postfix 2.8 and earlier the default is “ipv4”. For backwards
compatibility with these releases, the Postfix 2.9 and later upgrade
procedure appends an explicit “inet_protocols = ipv4″ setting to
main.cf when no explicit setting is present. This compatibility
workaround will be phased out as IPv6 deployment becomes more common.

This feature is available in Postfix 2.2 and later.

Note: you MUST stop and start Postfix after changing this
parameter.

On systems that pre-date IPV6_V6ONLY support (RFC 3493), an
IPv6 server will also accept IPv4 connections, even when IPv4 is
turned off with the inet_protocols parameter. On systems with
IPV6_V6ONLY support, Postfix will use separate server sockets for
IPv6 and IPv4, and each will accept only connections for the
corresponding protocol.

When IPv4 support is enabled via the inet_protocols parameter,
Postfix will look up DNS type A records, and will convert
IPv4-in-IPv6 client IP addresses (::ffff:1.2.3.4) to their original
IPv4 form (1.2.3.4). The latter is needed on hosts that pre-date
IPV6_V6ONLY support (RFC 3493).

When IPv6 support is enabled via the inet_protocols parameter,
Postfix will do DNS type AAAA record lookups.

When both IPv4 and IPv6 support are enabled, the Postfix SMTP
client will choose the protocol as specified with the
smtp_address_preference parameter. Postfix versions before 2.8
attempt to connect via IPv6 before attempting to use IPv4.

Examples:

inet_protocols = ipv4
inet_protocols = all (DEFAULT)
inet_protocols = ipv6
inet_protocols = ipv4, ipv6

(default: external)

The email address form that will be used in non-debug logging
(info, warning, etc.). As of Postfix 3.5 when an address localpart
contains spaces or other special characters, the localpart will be
quoted, for example:

    from=<"name with spaces"@example.com>

Older Postfix versions would log the internal (unquoted) form:

    from=<name with spaces@example.com>

The external and internal forms are identical for the vast
majority of email addresses that contain no spaces or other special
characters in the localpart.

The logging in external form is consistent with the address
form that Postfix 3.2 and later prefer for most table lookups. This
is therefore the more useful form for non-debug logging.

Specify “info_log_address_format = internal” for backwards
compatibility.

Postfix uses the unquoted form internally, because an attacker
can specify an email address in different forms by playing games
with quotes and backslashes. An attacker should not be able to use
such games to circumvent Postfix access policies.

This feature is available in Postfix 3.5 and later.


(default: 5)

The initial per-destination concurrency level for parallel delivery
to the same destination.
With per-destination recipient limit > 1, a destination is a domain,
otherwise it is a recipient.

Use transport_initial_destination_concurrency to specify
a transport-specific override, where transport is the master.cf
name of the message delivery transport (Postfix 2.5 and later).

Warning: with concurrency of 1, one bad message can be enough to
block all mail to a site.


(default: empty)

What categories of Postfix-generated mail are subject to
before-queue content inspection by non_smtpd_milters, header_checks
and body_checks. Specify zero or more of the following, separated
by whitespace or comma.

bounce
Inspect the content of delivery
status notifications.
notify
Inspect the content of postmaster
notifications by the smtp(8) and smtpd(8) processes.

NOTE: It’s generally not safe to enable content inspection of
Postfix-generated email messages. The user is warned.

This feature is available in Postfix 2.3 and later.


(default: 501)

The numerical Postfix SMTP server response code when the client
HELO or EHLO command parameter is rejected by the reject_invalid_helo_hostname
restriction.

Do not change this unless you have a complete understanding of RFC 5321.


(default: version dependent)

The time after which a client closes an idle internal communication
channel. The purpose is to allow Postfix daemon processes to
terminate voluntarily after they become idle. This is used, for
example, by the Postfix address resolving and rewriting clients.

With Postfix 2.4 the default value was reduced from 100s to 5s.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 3600s)

The time limit for sending or receiving information over an internal
communication channel. The purpose is to break out of deadlock
situations. If the time limit is exceeded the software aborts with a
fatal error.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 1000s)

The time after which a client closes an active internal communication
channel. The purpose is to allow Postfix daemon processes to
terminate voluntarily
after reaching their client limit. This is used, for example, by
the Postfix address resolving and rewriting clients.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: lmtp=24, smtp=25, smtps=submissions=465, submission=587)

Optional setting that avoids lookups in the services(5) database.
This feature was implemented to address inconsistencies in the name
of the port “465” service. The ABNF is:

known_tcp_ports = empty | name-to-port *(“,” name-to-port)
name-to-port = 1*(service-name “=’) port-number

The comma is required. Whitespace is optional but it cannot appear
inside a service name or port number.

This feature is available in Postfix 3.6 and later.


(default: 2048)

Upon input, long lines are chopped up into pieces of at most
this length; upon delivery, long lines are reconstructed.


(default: 16777216)

The initial OpenLDAP LMDB database size limit in bytes. Each time
a database becomes full, its size limit is doubled.

This feature is available in Postfix 2.11 and later.


(default: ipv6)

The LMTP-specific version of the smtp_address_preference
configuration parameter. See there for details.

This feature is available in Postfix 2.8 and later.


(default: rcpt)

The LMTP-specific version of the smtp_address_verify_target
configuration parameter. See there for details.

This feature is available in Postfix 3.0 and later.


(default: no)

When a remote LMTP server announces no DSN support, assume that
the
server performs final delivery, and send “delivered” delivery status
notifications instead of “relayed”. The default setting is backwards
compatible to avoid the infinitesimal possibility of breaking
existing LMTP-based content filters.


(default: yes)

The LMTP-specific version of the smtp_balance_inet_protocols
configuration parameter. See there for details.

This feature is available in Postfix 3.3 and later.


(default: empty)

The LMTP-specific version of the smtp_bind_address configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_bind_address6 configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_bind_address_enforce
configuration parameter. See there for details.

This feature is available in Postfix 3.7 and later.


(default: empty)

The LMTP-specific version of the smtp_body_checks configuration
parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: yes)

Keep Postfix LMTP client connections open for up to $max_idle
seconds. When the LMTP client receives a request for the same
connection the connection is reused.

This parameter is available in Postfix version 2.2 and earlier.
With Postfix version 2.3 and later, see lmtp_connection_cache_on_demand,
lmtp_connection_cache_destinations, or lmtp_connection_reuse_time_limit.

The effectiveness of cached connections will be determined by the
number of remote LMTP servers in use, and the concurrency limit specified
for the Postfix LMTP client. Cached connections are closed under any of
the following conditions:

Most of these limitations have been with the Postfix
connection cache that is shared among multiple LMTP client
programs.


(default: yes)

The LMTP-specific version of the smtp_cname_overrides_servername
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 0s)

The Postfix LMTP client time limit for completing a TCP connection, or
zero (use the operating system built-in time limit). When no
connection can be made within the deadline, the LMTP client tries
the next address on the mail exchanger list.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

Example:

lmtp_connect_timeout = 30s

(default: empty)

The LMTP-specific version of the smtp_connection_cache_destinations
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: yes)

The LMTP-specific version of the smtp_connection_cache_on_demand
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 2s)

The LMTP-specific version of the
smtp_connection_cache_time_limit configuration parameter.
See there for details.

This feature is available in Postfix 2.3 and later.


(default: 0)

The LMTP-specific version of the smtp_connection_reuse_count_limit
configuration parameter. See there for details.

This feature is available in Postfix 2.11 and later.


(default: 300s)

The LMTP-specific version of the smtp_connection_reuse_time_limit
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 600s)

The Postfix LMTP client time limit for sending the LMTP “.”,
and for receiving the remote LMTP server response. When no response
is received within the deadline, a warning is logged that the mail
may be delivered multiple times.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 120s)

The Postfix LMTP client time limit for sending the LMTP DATA command,
and
for receiving the remote LMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 180s)

The Postfix LMTP client time limit for sending the LMTP message
content.
When the connection stalls for more than $lmtp_data_xfer_timeout
the LMTP client terminates the transfer.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: no)

The LMTP-specific version of the smtp_defer_if_no_mx_address_found
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_delivery_status_filter
configuration parameter. See there for details.

This feature is available in Postfix 3.0 and later.


(default: $default_destination_concurrency_limit)

The maximal number of parallel deliveries to the same destination
via the lmtp message delivery transport. This limit is enforced by
the queue manager. The message delivery transport name is the first
field in the entry in the master.cf file.


(default: $default_destination_recipient_limit)

The maximal number of recipients per message for the lmtp
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.

Setting this parameter to a value of 1 changes the meaning of
lmtp_destination_concurrency_limit from concurrency per domain into
concurrency per recipient.


(default: empty)

Lookup tables, indexed by the remote LMTP server address, with
case insensitive lists of LHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix LMTP client will ignore in the LHLO
response
from a remote LMTP server. See lmtp_discard_lhlo_keywords for
details. The table is not indexed by hostname for consistency with
smtpd_discard_ehlo_keyword_address_maps.

This feature is available in Postfix 2.3 and later.


(default: empty)

A case insensitive list of LHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix LMTP client will ignore in the LHLO
response
from a remote LMTP server.

This feature is available in Postfix 2.3 and later.

Notes:


(default: empty)

Optional filter for Postfix LMTP client DNS lookup results.
See smtp_dns_reply_filter for details including an example.

This feature is available in Postfix 3.0 and later.


(default: empty)

The LMTP-specific version of the smtp_dns_resolver_options
configuration parameter. See there for details.

This feature is available in Postfix 2.8 and later.


(default: empty)

The LMTP-specific version of the smtp_dns_support_level
configuration parameter. See there for details.

This feature is available in Postfix 2.11 and later.


(default: no)

The LMTP-specific version of the smtp_enforce_tls configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

Optional list of relay hosts for LMTP destinations that can’t be
found or that are unreachable. In main.cf elements are separated by
whitespace or commas.

By default, mail is returned to the sender when a destination is not
found, and delivery is deferred when a destination is unreachable.

The fallback relays must be TCP destinations, specified without
a leading “inet:” prefix. Specify a host or host:port. Since MX
lookups do not apply with LMTP, there is no need to use the “[host]” or
“[host]:port” forms. If you specify multiple LMTP destinations, Postfix
will try them in the specified order.

This feature is available in Postfix 3.1 and later.


(default: empty)

The LMTP-specific version of the smtp_generic_maps configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_header_checks configuration
parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: dns)

The LMTP-specific version of the smtp_host_lookup configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: $myhostname)

The hostname to send in the LMTP LHLO command.

The default value is the machine hostname. Specify a hostname or
[ip.add.re.ss] or [ip:v6:add:re::ss].

This information can be specified in the main.cf file for all LMTP
clients, or it can be specified in the master.cf file for a specific
client, for example:

/etc/postfix/master.cf:
    mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

This feature is available in Postfix 2.3 and later.


(default: 300s)

The Postfix LMTP client time limit for sending the LHLO command,
and for receiving the initial remote LMTP server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). The default time unit is s (seconds).


(default: 990)

The LMTP-specific version of the smtp_line_length_limit
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 300s)

The Postfix LMTP client time limit for sending the MAIL FROM command,
and for receiving the remote LMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

The LMTP-specific version of the smtp_mime_header_checks
configuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: 500)

The LMTP-specific version of the smtp_min_data_rate configuration
parameter. See there for details.

This feature is available in Postfix 3.7 and later.


(default: 5)

The LMTP-specific version of the smtp_mx_address_limit configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 2)

The LMTP-specific version of the smtp_mx_session_limit configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_nested_header_checks
configuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: no)

The LMTP-specific version of the smtp_per_record_deadline
configuration parameter. See there for details.

This feature is available in Postfix 2.9 and later.


(default: no)

The LMTP-specific version of the smtp_per_request_deadline
configuration parameter. See there for details.

This feature is available in Postfix 3.7 and later.


(default: 10s)

The LMTP-specific version of the smtp_pix_workaround_delay_time
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_pix_workaround_maps
configuration parameter. See there for details.

This feature is available in Postfix 2.4 and later.


(default: 500s)

The LMTP-specific version of the smtp_pix_workaround_threshold_time
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_pix_workaround
configuration parameter. See there for details.

This feature is available in Postfix 2.4 and later.


(default: 300s)

The Postfix LMTP client time limit for sending the QUIT command,
and for receiving the remote LMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: yes)

The LMTP-specific version of the smtp_quote_rfc821_envelope
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: yes)

The LMTP-specific version of the smtp_randomize_addresses
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 300s)

The Postfix LMTP client time limit for sending the RCPT TO command,
and for receiving the remote LMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

The LMTP-specific version of the smtp_reply_filter
configuration parameter. See there for details.

This feature is available in Postfix 2.7 and later.


(default: 20s)

The Postfix LMTP client time limit for sending the RSET command,
and for receiving the remote LMTP server response. The LMTP client
sends RSET in
order to finish a recipient address probe, or to verify that a
cached connection is still alive.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

The LMTP-specific version of the smtp_sasl_auth_cache_name
configuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: 90d)

The LMTP-specific version of the smtp_sasl_auth_cache_time
configuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: no)

Enable SASL authentication in the Postfix LMTP client.


(default: yes)

The LMTP-specific version of the smtp_sasl_auth_soft_bounce
configuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: empty)

The LMTP-specific version of the smtp_sasl_mechanism_filter
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

Optional Postfix LMTP client lookup tables with one username:password entry
per host or domain. If a remote host or domain has no username:password
entry, then the Postfix LMTP client will not attempt to authenticate
to the remote host.


(default: empty)

Implementation-specific information that is passed through to
the SASL plug-in implementation that is selected with
lmtp_sasl_type. Typically this specifies the name of a
configuration file or rendezvous point.

This feature is available in Postfix 2.3 and later.


(default: noplaintext, noanonymous)

SASL security options; as of Postfix 2.3 the list of available
features depends on the SASL client implementation that is selected
with lmtp_sasl_type.

The following security features are defined for the cyrus
client SASL implementation:

noplaintext
Disallow authentication methods that use plaintext passwords.
noactive
Disallow authentication methods that are vulnerable to non-dictionary
active attacks.
nodictionary
Disallow authentication methods that are vulnerable to passive
dictionary attacks.
noanonymous
Disallow anonymous logins.

Example:

lmtp_sasl_security_options = noplaintext

(default: $lmtp_sasl_security_options)

The LMTP-specific version of the smtp_sasl_tls_security_options
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: $lmtp_sasl_tls_security_options)

The LMTP-specific version of the
smtp_sasl_tls_verified_security_options configuration parameter.
See there for details.

This feature is available in Postfix 2.3 and later.


(default: cyrus)

The SASL plug-in type that the Postfix LMTP client should use
for authentication. The available types are listed with the
postconf -A” command.

This feature is available in Postfix 2.3 and later.


(default: no)

The LMTP-specific version of the smtp_send_dummy_mail_auth
configuration parameter. See there for details.

This feature is available in Postfix 2.9 and later.


(default: no)

Send an XFORWARD command to the remote LMTP server when the LMTP LHLO
server response announces XFORWARD support. This allows an lmtp(8)
delivery agent, used for content filter message injection, to
forward the name, address, protocol and HELO name of the original
client to the content filter and downstream LMTP server.
Before you change the value to yes, it is best to make sure that
your content filter supports this command.

This feature is available in Postfix 2.1 and later.


(default: no)

The LMTP-specific version of the smtp_sender_dependent_authentication
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: yes)

The LMTP-specific version of the smtp_skip_5xx_greeting
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: no)

Wait for the response to the LMTP QUIT command.


(default: 300s)

The LMTP-specific version of the smtp_starttls_timeout configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 24)

The default TCP port that the Postfix LMTP client connects to.
Specify a symbolic name (see services(5)) or a numeric port.


(default: empty)

The LMTP-specific version of the smtp_tls_CAfile
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_CApath
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_block_early_mail_reply
configuration parameter. See there for details.

This feature is available in Postfix 2.7 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_cert_file
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_chain_files configuration
parameter. See there for details.

This feature is available in Postfix 3.4 and later.


(default: medium)

The LMTP-specific version of the smtp_tls_ciphers configuration
parameter. See there for details.

This feature is available in Postfix 2.6 and later.


(default: no)

The LMTP-specific version of the smtp_tls_connection_reuse configuration
parameter. See there for details.

This feature is available in Postfix 3.4 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_dcert_file
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: $lmtp_tls_dcert_file)

The LMTP-specific version of the smtp_tls_dkey_file
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_eccert_file configuration
parameter. See there for details.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.


(default: empty)

The LMTP-specific version of the smtp_tls_eckey_file configuration
parameter. See there for details.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.


(default: yes)

The LMTP-specific version of the smtp_tls_enforce_peername
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_exclude_ciphers
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_fingerprint_cert_match
configuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: see “postconf -d” output)

The LMTP-specific version of the smtp_tls_fingerprint_digest
configuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.


(default: no)

The LMTP-specific version of the smtp_tls_force_insecure_host_tlsa_lookup
configuration parameter. See there for details.

This feature is available in Postfix 2.11 and later.


(default: $lmtp_tls_cert_file)

The LMTP-specific version of the smtp_tls_key_file
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 0)

The LMTP-specific version of the smtp_tls_loglevel
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: medium)

The LMTP-specific version of the smtp_tls_mandatory_ciphers
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_mandatory_exclude_ciphers
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: see postconf -d output)

The LMTP-specific version of the smtp_tls_mandatory_protocols
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: no)

The LMTP-specific version of the smtp_tls_note_starttls_offer
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_per_site configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_policy_maps
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: see postconf -d output)

The LMTP-specific version of the smtp_tls_protocols configuration
parameter. See there for details.

This feature is available in Postfix 2.6 and later.


(default: 9)

The LMTP-specific version of the smtp_tls_scert_verifydepth
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: nexthop)

The LMTP-specific version of the smtp_tls_secure_cert_match
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_security_level configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_servername configuration
parameter. See there for details.

This feature is available in Postfix 3.4 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_session_cache_database
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 3600s)

The LMTP-specific version of the smtp_tls_session_cache_timeout
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: empty)

The LMTP-specific version of the smtp_tls_trust_anchor_file
configuration parameter. See there for details.

This feature is available in Postfix 2.11 and later.


(default: hostname)

The LMTP-specific version of the smtp_tls_verify_cert_match
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: no)

The LMTP-specific version of the smtp_tls_wrappermode configuration
parameter. See there for details.

This feature is available in Postfix 3.0 and later.


(default: no)

The LMTP-specific version of the smtp_use_tls configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.


(default: 300s)

The Postfix LMTP client time limit for sending the XFORWARD command,
and for receiving the remote LMTP server response.

In case of problems the client does NOT try the next address on
the mail exchanger list.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: empty)

Optional shell program for local(8) delivery to non-Postfix commands.
By default, non-Postfix commands are executed directly; commands
are given to the default shell (typically, /bin/sh) only when they
contain shell meta characters or shell built-in commands.

“sendmail’s restricted shell” (smrsh) is what most people will
use in order to restrict what programs can be run from e.g. .forward
files (smrsh is part of the Sendmail distribution).

Note: when a shell program is specified, it is invoked even
when the command contains no shell built-in commands or meta
characters.

Example:

local_command_shell = /some/where/smrsh -c
local_command_shell = /bin/bash -c

(default: $default_delivery_status_filter)

Optional filter for the local(8) delivery agent to change the
status code or explanatory text of successful or unsuccessful
deliveries. See default_delivery_status_filter for details.

This feature is available in Postfix 3.0 and later.


(default: 2)

The maximal number of parallel deliveries via the local mail
delivery transport to the same recipient (when
local_destination_recipient_limit = 1″) or the maximal number of
parallel deliveries to the same local domain (when
local_destination_recipient_limit > 1″). This limit is enforced by
the queue manager. The message delivery transport name is the first
field in the entry in the master.cf file.

A low limit of 2 is recommended, just in case someone has an
expensive shell command in a .forward file or in an alias (e.g.,
a mailing list manager). You don’t want to run lots of those at
the same time.


(default: 1)

The maximal number of recipients per message delivery via the
local mail delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.

Setting this parameter to a value > 1 changes the meaning of
local_destination_concurrency_limit from concurrency per recipient
into concurrency per domain.


(default: permit_inet_interfaces)

Rewrite message header addresses in mail from these clients and
update incomplete addresses with the domain name in $myorigin or
$mydomain; either don’t rewrite message headers from other clients
at all, or rewrite message headers and update incomplete addresses
with the domain specified in the remote_header_rewrite_domain
parameter.

See the append_at_myorigin and append_dot_mydomain parameters
for details of how domain names are appended to incomplete addresses.

Specify a list of zero or more of the following:

permit_inet_interfaces
Append the domain name in $myorigin or $mydomain when the
client IP address matches $inet_interfaces. This is enabled by
default.
permit_mynetworks
Append the domain name in $myorigin or $mydomain when the
client IP address matches any network or network address listed in
$mynetworks. This setting will not prevent remote mail header
address rewriting when mail from a remote client is forwarded by
a neighboring system.
permit_sasl_authenticated
Append the domain name in $myorigin or $mydomain when the
client is successfully authenticated via the RFC 4954 (AUTH)
protocol.
permit_tls_clientcerts
Append the domain name in $myorigin or $mydomain when the
remote SMTP client TLS certificate fingerprint or public key fingerprint
(Postfix 2.9 and later) is listed in $relay_clientcerts.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5).
The default algorithm is sha256 with Postfix ≥ 3.6
and the compatibility_level set to 3.6 or higher. With Postfix
≤ 3.5, the default algorithm is md5. The best-practice
algorithm is now sha256. Recent advances in hash function
cryptanalysis have led to md5 and sha1 being deprecated in favor of
sha256. However, as long as there are no known “second pre-image”
attacks against the older algorithms, their use in this context, though
not recommended, is still likely safe.
permit_tls_all_clientcerts
Append the domain name in $myorigin or $mydomain when the
remote SMTP client TLS certificate is successfully verified, regardless of
whether it is listed on the server, and regardless of the certifying
authority.
type:table
type:table
Append the domain name in $myorigin or $mydomain when the
client IP address matches the specified lookup table.
The lookup result is ignored, and no subnet lookup is done. This
is suitable for, e.g., pop-before-smtp lookup tables.

Examples:

The Postfix < 2.2 backwards compatible setting: always rewrite
message headers, and always append my own domain to incomplete
header addresses.

local_header_rewrite_clients = static:all

The purist (and default) setting: rewrite headers only in mail
from Postfix sendmail and in SMTP mail from this machine.

local_header_rewrite_clients = permit_inet_interfaces

The intermediate setting: rewrite header addresses and append
$myorigin or $mydomain information only with mail from Postfix
sendmail, from local clients, or from authorized SMTP clients.

Note: this setting will not prevent remote mail header address
rewriting when mail from a remote client is forwarded by a neighboring
system.

local_header_rewrite_clients = permit_mynetworks,
    permit_sasl_authenticatedpermit_tls_clientcertscheck_address_maphash:/etc/postfix/pop-before-smtp


(default: static:*)

A list of lookup tables that are searched by the UNIX login name,
and that return a list of allowed envelope sender patterns separated
by space or comma. These sender patterns are enforced by the Postfix
postdrop(1) command. The default is backwards-compatible:
every user may specify any sender envelope address.

When no UNIX login name is available, the postdrop(1) command will
prepend “uid:” to the numerical UID and use that instead.

This feature ignores address extensions in the user-specified
envelope sender address.

The following sender patterns are special; these cannot be used
as part of a longer pattern.

*
This pattern allows any envelope sender address.
<>
This pattern allows the empty
envelope sender address. See the
empty_address_local_login_sender_maps_lookup_key configuration
parameter.
@domain
This pattern allows an
envelope sender address when the ‘@‘ and domain part
match.

Examples:

/etc/postfix/main.cf:
    # Allow root and postfix full control, anyone else can only
    # send mail as themselves. Use "uid:" followed by the numerical
    # UID when the UID has no entry in the UNIX password file.
    local_login_sender_maps =
        inline:{ { root = * }, { postfix = * } },
        pcre:/etc/postfix/login_senders
/etc/postfix/login_senders:
   # Allow both the bare username and the user@domain forms.
    /(. )/ $1 $1@example.com

This feature is available in Postfix 3.6 and later.


(default: proxy:unix:passwd.byname $alias_maps)

Lookup tables with all names or addresses of local recipients:
a recipient address is local when its domain matches $mydestination,
$inet_interfaces or $proxy_interfaces. Specify @domain as a
wild-card for domains that do not have a valid recipient list.
Technically, tables listed with $local_recipient_maps are used as
lists: Postfix needs to know only if a lookup string is found or
not, but it does not use the result from table lookup.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

If this parameter is non-empty (the default), then the Postfix SMTP
server will reject mail for unknown local users.

To turn off local recipient checking in the Postfix SMTP server,
specify “local_recipient_maps =” (i.e. empty).

The default setting assumes that you use the default Postfix local
delivery agent for local delivery. You need to update the
local_recipient_maps setting if:

Details are described in the LOCAL_RECIPIENT_README file.

Beware: if the Postfix SMTP server runs chrooted, you need to access
the passwd file via the proxymap(8) service, in order to overcome
chroot access restrictions. The alternative, maintaining a copy of
the system password file in the chroot jail is not practical.

Examples:

local_recipient_maps =

(default: local:$myhostname)

The default mail delivery transport and next-hop destination
for final delivery to domains listed with mydestination, and for
[ipaddress] destinations that match $inet_interfaces or $proxy_interfaces.
This information can be overruled with the transport(5) table.

By default, local mail is delivered to the transport called “local”,
which is just the name of a service that is defined the master.cf file.

Specify a string of the form transport:nexthop, where transport
is the name of a mail delivery transport defined in master.cf.
The :nexthop destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent.

Beware: if you override the default local delivery agent then you
need to review the LOCAL_RECIPIENT_README document, otherwise the
SMTP server may reject mail for local recipients.


(default: empty)

Optional catch-all destination for unknown local(8) recipients.
By default, mail for unknown recipients in domains that match
$mydestination, $inet_interfaces or $proxy_interfaces is returned
as undeliverable.

The luser_relay value is not subject to Postfix configuration
parameter $name expansion. Instead, the following $name expansions
are done:

$domain
The recipient domain.
$extension
The recipient address extension.
$home
The recipient’s home directory.
$local
The entire recipient address localpart.
$recipient
The full recipient address.
$recipient_delimiter
The address extension delimiter that was found in the recipient
address (Postfix 2.11 and later), or the system-wide recipient
address extension delimiter (Postfix 2.10 and earlier).
$shell
The recipient’s login shell.
$user
The recipient username.
${name?value}
${name?{value}} (Postfix ≥ 3.0)
Expands to value when $name is non-empty.
${name:value}
${name:{value}} (Postfix ≥ 3.0)
Expands to value when $name is empty.
${name?{value1}:{value2}} (Postfix ≥ 3.0)
Expands to value1 when $name is non-empty,
value2 otherwise.

Instead of $name you can also specify ${name} or $(name).

Note: luser_relay works only for the Postfix local(8) delivery agent.

Note: if you use this feature for accounts not in the UNIX password
file, then you must specify “local_recipient_maps =” (i.e. empty)
in the main.cf file, otherwise the Postfix SMTP server will reject mail
for non-UNIX accounts with “User unknown in local recipient table”.

Examples:

luser_relay = $user@other.host
luser_relay = $local@other.host
luser_relay = admin $local

(default: Postfix)

The mail system name that is displayed in Received: headers, in
the SMTP greeting banner, and in bounced mail.


(default: postfix)

The UNIX system account that owns the Postfix queue and most Postfix
daemon processes. Specify the name of an unprivileged user account
that does not share a user or group ID with other accounts, and that
owns no other files
or processes on the system. In particular, don’t specify nobody
or daemon. PLEASE USE A DEDICATED USER ID AND GROUP ID.

When this parameter value is changed you need to re-run “postfix
set-permissions
” (with Postfix version 2.0 and earlier:
/etc/postfix/post-install set-permissions“.


(default: see “postconf -d” output)

The Postfix release date, in “YYYYMMDD” format.


(default: see “postconf -d” output)

The directory where local(8) UNIX-style mailboxes are kept. The
default setting depends on the system type. Specify a name ending
in / for maildir-style delivery.

Note: maildir delivery is done with the privileges of the recipient.
If you use the mail_spool_directory setting for maildir style
delivery, then you must create the top-level maildir directory in
advance. Postfix will not create it.

Examples:

mail_spool_directory = /var/mail
mail_spool_directory = /var/spool/mail

(default: see “postconf -d” output)

The version of the mail system. Stable releases are named
major.minor.patchlevel. Experimental releases
also include the release date. The version string can be used in,
for example, the SMTP greeting banner.


(default: empty)

Optional external command that the local(8) delivery agent should
use for mailbox delivery. The command is run with the user ID and
the primary group ID privileges of the recipient. Exception:
command delivery for root executes with $default_privs privileges.
This is not a problem, because 1) mail for root should always be
aliased to a real user and 2) don’t log in as root, use “su” instead.

The following environment variables are exported to the command:

CLIENT_ADDRESS
Remote client network address. Available in Postfix version 2.2 and
later.
CLIENT_HELO
Remote client EHLO command parameter. Available in Postfix version 2.2
and later.
CLIENT_HOSTNAME
Remote client hostname. Available in Postfix version 2.2 and later.
CLIENT_PROTOCOL
Remote client protocol. Available in Postfix version 2.2 and later.
DOMAIN
The domain part of the recipient address.
EXTENSION
The optional address extension.
HOME
The recipient home directory.
LOCAL
The recipient address localpart.
LOGNAME
The recipient’s username.
ORIGINAL_RECIPIENT
The entire recipient address, before any address rewriting or
aliasing.
RECIPIENT
The full recipient address.
SASL_METHOD
SASL authentication method specified in the remote client AUTH
command. Available in Postfix version 2.2 and later.
SASL_SENDER
SASL sender address specified in the remote client MAIL FROM
command. Available in Postfix version 2.2 and later.
SASL_USER
SASL username specified in the remote client AUTH command.
Available in Postfix version 2.2 and later.
SENDER
The full sender address.
SHELL
The recipient’s login shell.
USER
The recipient username.

Unlike other Postfix configuration parameters, the mailbox_command
parameter is not subjected to $name substitutions. This is to make
it easier to specify shell syntax (see example below).

If you can, avoid shell meta characters because they will force
Postfix to run an expensive shell process. If you’re delivering
via “procmail” then running a shell won’t make a noticeable difference
in the total cost.

Note: if you use the mailbox_command feature to deliver mail
system-wide, you must set up an alias that forwards mail for root
to a real user.

The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.

Examples:

mailbox_command = /some/where/procmail
mailbox_command = /some/where/procmail -a "$EXTENSION"
mailbox_command = /some/where/maildrop -d "$USER"
        -f "$SENDER" "$EXTENSION"

(default: empty)

Optional lookup tables with per-recipient external commands to use
for local(8) mailbox delivery. Behavior is as with mailbox_command.

The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.


(default: see “postconf -d” output)

How to lock a UNIX-style local(8) mailbox before attempting delivery.
For a list of available file locking methods, use the “postconf
-l
” command.

This setting is ignored with maildir style delivery,
because such deliveries are safe without explicit locks.

Note: The dotlock method requires that the recipient UID or
GID has write access to the parent directory of the mailbox file.

Note: the default setting of this parameter is system dependent.


(default: 51200000)

The maximal size of any local(8) individual mailbox or maildir
file, or zero (no limit). In fact, this limits the size of any
file that is written to upon local delivery, including files written
by external commands that are executed by the local(8) delivery
agent. The value cannot exceed LONG_MAX (typically, a 32-bit or
64-bit signed integer).

This limit must not be smaller than the message size limit.


(default: empty)

Optional message delivery transport that the local(8) delivery
agent should use for mailbox delivery to all local recipients,
whether or not they are found in the UNIX passwd database.

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The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.


(default: empty)

Optional lookup tables with per-recipient message delivery
transports to use for local(8) mailbox delivery, whether or not the
recipients are found in the UNIX passwd database.

The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

For safety reasons, this feature does not allow $number
substitutions in regular expression maps.

This feature is available in Postfix 2.3 and later.


(default: empty)

The name of an optional logfile that is written by the Postfix
postlogd(8) service. An empty value selects logging to syslogd(8).
Specify “/dev/stdout” to select logging to standard output. Stdout
logging requires that Postfix is started with “postfix start-fg”.

Note 1: The maillog_file parameter value must contain a prefix
that is specified with the maillog_file_prefixes parameter.

Note 2: Some Postfix non-daemon programs may still log information
to syslogd(8), before they have processed their configuration
parameters and command-line options.

This feature is available in Postfix 3.4 and later.


(default: gzip)

The program to run after rotating $maillog_file with “postfix
logrotate”. The command is run with the rotated logfile name as its
first argument.

This feature is available in Postfix 3.4 and later.


(default: /var, /dev/stdout)

A list of allowed prefixes for a maillog_file value. This is a
safety feature to contain the damage from a single configuration
mistake. Specify one or more prefix strings, separated by comma or
whitespace.

This feature is available in Postfix 3.4 and later.


(default: %Y%m%d-%H%M%S)

The format of the suffix to append to $maillog_file while rotating
the file with “postfix logrotate”. See strftime(3) for syntax. The
default suffix, YYYYMMDD-HHMMSS, allows logs to be rotated frequently.

This feature is available in Postfix 3.4 and later.


(default: see “postconf -d” output)

Sendmail compatibility feature that specifies where the Postfix
mailq(1) command is installed. This command can be used to
list the Postfix mail queue.


(default: see “postconf -d” output)

Where the Postfix manual pages are installed.


(default: empty)

Obsolete feature: use the reject_rbl_client feature instead.


(default: 554)

The numerical Postfix SMTP server response code when a remote SMTP
client request is blocked by the reject_rbl_client, reject_rhsbl_client,
reject_rhsbl_reverse_client, reject_rhsbl_sender or
reject_rhsbl_recipient restriction.

Do not change this unless you have a complete understanding of RFC 5321.


(default: envelope_sender, header_sender, header_recipient)

What addresses are subject to address masquerading.

By default, address masquerading is limited to envelope sender
addresses, and to header sender and header recipient addresses.
This allows you to use address masquerading on a mail gateway while
still being able to forward mail to users on individual machines.

Specify zero or more of: envelope_sender, envelope_recipient,
header_sender, header_recipient


(default: empty)

Optional list of domains whose subdomain structure will be stripped
off in email addresses.

The list is processed left to right, and processing stops at the
first match. Thus,

masquerade_domains = foo.example.com example.com

strips “user@any.thing.foo.example.com” to “user@foo.example.com”,
but strips “user@any.thing.else.example.com” to “user@example.com”.

A domain name prefixed with ! means do not masquerade this domain
or its subdomains. Thus,

masquerade_domains = !foo.example.com example.com

does not change “user@any.thing.foo.example.com” or “user@foo.example.com”,
but strips “user@any.thing.else.example.com” to “user@example.com”.

Note: with Postfix version 2.2, message header address masquerading
happens only when message header address rewriting is enabled:

To get the behavior before Postfix version 2.2, specify
local_header_rewrite_clients = static:all”.

Example:

masquerade_domains = $mydomain

(default: empty)

Optional list of user names that are not subjected to address
masquerading, even when their addresses match $masquerade_domains.

By default, address masquerading makes no exceptions.

Specify a list of user names, “/file/name” or “type:table” patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A “/file/name”
pattern is replaced
by its contents; a “type:table” lookup table is matched when a name
matches a lookup key (the lookup result is ignored). Continue long
lines by starting the next line with whitespace. Specify “!pattern”
to exclude a name from the list. The form “!/file/name” is supported
only in Postfix version 2.4 and later.

Examples:

masquerade_exceptions = root, mailer-daemon
masquerade_exceptions = root

(default: empty)

Selectively disable master(8) listener ports by service type
or by service name and type. Specify a list of service types
(“inet”, “unix”, “fifo”, or “pass”) or “name/type” tuples, where
“name” is the first field of a master.cf entry and “type” is a
service type. As with other Postfix matchlists, a search stops at
the first match. Specify “!pattern” to exclude a service from the
list. By default, all master(8) listener ports are enabled.

Note: this feature does not support “/file/name” or “type:table
patterns, nor does it support wildcards such as “*” or “all”. This
is intentional.

Examples:

# With Postfix 2.6..2.10 use '.' instead of '/'.
# Turn on all master(8) listener ports (the default).
master_service_disable =
# Turn off only the main SMTP listener port.
master_service_disable = smtp/inet
# Turn off all TCP/IP listener ports.
master_service_disable = inet
# Turn off all TCP/IP listener ports except "foo".
master_service_disable = !foo/inet, inet

This feature is available in Postfix 2.6 and later.


(default: 100s)

The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily. This
parameter
is ignored by the Postfix queue manager and by other long-lived
Postfix daemon processes.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 100)

The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily. This parameter
is ignored by the Postfix queue
manager and by other long-lived Postfix daemon processes.


(default: 4000s)

The maximal time between attempts to deliver a deferred message.

This parameter should be set to a value greater than or equal
to $minimal_backoff_time. See also $queue_run_delay.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 5d)

Consider a message as undeliverable, when delivery fails with a
temporary error, and the time in the queue has reached the
maximal_queue_lifetime limit.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

Specify 0 when mail delivery should be tried only once.


(default: bcc, content-length, resent-bcc, return-path)

Names of message headers that the cleanup(8) daemon will remove
after applying header_checks(5) and before invoking Milter applications.
The default setting is compatible with Postfix < 3.0.

Specify a list of header names, separated by comma or space.
Names are matched in a case-insensitive manner. The list of supported
header names is limited only by available memory.

This feature is available in Postfix 3.0 and later.


(default: empty)

The set of characters that Postfix will reject in message
content. The usual C-like escape sequences are recognized: a
b f n r t v ddd
(up to three octal digits) and
\.

Note 1: this feature does not recognize text that requires MIME
decoding. It inspects raw message content, just like header_checks
and body_checks.

Note 2: this feature is disabled with “receive_override_options
= no_header_body_checks“.

Example:

message_reject_characters = 

This feature is available in Postfix 2.3 and later.


(default: 10240000)

The maximal size in bytes of a message, including envelope information.
The value cannot exceed LONG_MAX (typically, a 32-bit or 64-bit
signed integer).

Note: be careful when making changes. Excessively small values
will result in the loss of non-delivery notifications, when a bounce
message size exceeds the local or remote MTA’s message size limit.


(default: empty)

The set of characters that Postfix will remove from message
content. The usual C-like escape sequences are recognized: a
b f n r t v ddd
(up to three octal digits) and
\.

Note 1: this feature does not recognize text that requires MIME
decoding. It inspects raw message content, just like header_checks
and body_checks.

Note 2: this feature is disabled with “receive_override_options
= no_header_body_checks“.

Example:

message_strip_characters = 

This feature is available in Postfix 2.3 and later.


(default: see ‘postconf -d’ output)

The location of non-executable files that are shared among
multiple Postfix instances, such as postfix-files, dynamicmaps.cf,
and the multi-instance template files main.cf.proto and master.cf.proto.
This directory should contain only Postfix-related files. Typically,
the meta_directory parameter has the same default as the config_directory
parameter (/etc/postfix or /usr/local/etc/postfix).

For backwards compatibility with Postfix versions 2.6..2.11,
specify “meta_directory = $daemon_directory” in main.cf before
installing or upgrading Postfix, or specify “meta_directory =
/path/name” on the “make makefiles”, “make install” or “make upgrade”
command line.

This feature is available in Postfix 3.0 and later.


(default: 30s)

The time limit for sending an SMTP command to a Milter (mail
filter) application, and for receiving the response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The macros that are sent to Milter (mail filter) applications
after completion of an SMTP connection. See MILTER_README
for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.


(default: 30s)

The time limit for connecting to a Milter (mail filter)
application, and for negotiating protocol options.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.3 and later.


(default: 300s)

The time limit for sending message content to a Milter (mail
filter) application, and for receiving the response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The macros that are sent to version 4 or higher Milter (mail
filter) applications after the SMTP DATA command. See MILTER_README
for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.


(default: tempfail)

The default action when a Milter (mail filter) response is
unavailable (for example, bad Postfix configuration or Milter
failure). Specify one of the following:

accept
Proceed as if the mail filter was not present.
reject
Reject all further commands in this session
with a permanent status code.
tempfail
Reject all further commands in this session
with a temporary status code.
quarantine
Like “accept”, but freeze the message in
the “hold” queue. Available with Postfix 2.6 and later.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The macros that are sent to Milter (mail filter) applications
after the message end-of-data. See MILTER_README for a list of
available macro names and their meanings.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The macros that are sent to Milter (mail filter) applications
after the end of the message header. See MILTER_README for a list
of available macro names and their meanings.

This feature is available in Postfix 2.5 and later.


(default: empty)

Optional lookup tables for content inspection of message headers
that are produced by Milter applications. See the header_checks(5)
manual page available actions. Currently, PREPEND is not implemented.

The following example sends all mail that is marked as SPAM to
a spam handling machine. Note that matches are case-insensitive
by default.

/etc/postfix/main.cf:
    milter_header_checks = pcre:/etc/postfix/milter_header_checks
/etc/postfix/milter_header_checks:
    /^X-SPAM-FLAG:s YES/ FILTER mysmtp:sanitizer.example.com:25

The milter_header_checks mechanism could also be used for
allowlisting. For example it could be used to skip heavy content
inspection for DKIM-signed mail from known friendly domains.

This feature is available in Postfix 2.7, and as an optional
patch for Postfix 2.6.


(default: see “postconf -d” output)

The macros that are sent to Milter (mail filter) applications
after the SMTP HELO or EHLO command. See
MILTER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.


(default: $myhostname)

The {daemon_name} macro value for Milter (mail filter) applications.
See MILTER_README for a list of available macro names and their
meanings.

This feature is available in Postfix 2.3 and later.


(default: empty)

Optional list of name=value pairs that specify default
values for arbitrary macros that Postfix may send to Milter
applications. These defaults are used when there is no corresponding
information from the message delivery context.

Specify name=value or {name=value} pairs separated
by comma or whitespace. Enclose a pair in “{}” when a value contains
comma or whitespace (this form ignores whitespace after the enclosing
“{“, around the “=”, and before the enclosing “}”).

This feature is available in Postfix 3.1 and later.


(default: $mail_name $mail_version)

The {v} macro value for Milter (mail filter) applications.
See MILTER_README for a list of available macro names and their
meanings.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The macros that are sent to Milter (mail filter) applications
after the SMTP MAIL FROM command. See MILTER_README
for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.


(default: 6)

The mail filter protocol version and optional protocol extensions
for communication with a Milter application; prior to Postfix 2.6
the default protocol is 2. Postfix
sends this version number during the initial protocol handshake.
It should match the version number that is expected by the mail
filter application (or by its Milter library).

Protocol versions:

2
Use Sendmail 8 mail filter protocol version 2 (default
with Sendmail version 8.11 .. 8.13 and Postfix version 2.3 ..
2.5).
3
Use Sendmail 8 mail filter protocol version 3.
4
Use Sendmail 8 mail filter protocol version 4.
6
Use Sendmail 8 mail filter protocol version 6 (default
with Sendmail version 8.14 and Postfix version 2.6).

Protocol extensions:

no_header_reply
Specify this when the Milter application
will not reply for each individual message header.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The macros that are sent to Milter (mail filter) applications
after the SMTP RCPT TO command. See MILTER_README
for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The macros that are sent to version 3 or higher Milter (mail
filter) applications after an unknown SMTP command. See MILTER_README
for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.


(default: 2048)

The maximal length of MIME multipart boundary strings. The MIME
processor is unable to distinguish between boundary strings that
do not differ in the first $mime_boundary_length_limit characters.

This feature is available in Postfix 2.0 and later.


(default: $header_checks)

Optional lookup tables for content inspection of MIME related
message headers, as described in the header_checks(5) manual page.

This feature is available in Postfix 2.0 and later.


(default: 100)

The maximal recursion level that the MIME processor will handle.
Postfix refuses mail that is nested deeper than the specified limit.

This feature is available in Postfix 2.0 and later.


(default: 300s)

The minimal time between attempts to deliver a deferred message;
prior to Postfix 2.4 the default value was 1000s.

This parameter also limits the time an unreachable destination is
kept in the short-term, in-memory, destination status cache.

This parameter should be set greater than or equal to
$queue_run_delay. See also $maximal_backoff_time.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

An optional list of non-default Postfix configuration directories;
these directories belong to additional Postfix instances that share
the Postfix executable files and documentation with the default
Postfix instance, and that are started, stopped, etc., together
with the default Postfix instance. Specify a list of pathnames
separated by comma or whitespace.

When $multi_instance_directories is empty, the postfix(1) command
runs in single-instance mode and operates on a single Postfix
instance only. Otherwise, the postfix(1) command runs in multi-instance
mode and invokes the multi-instance manager specified with the
multi_instance_wrapper parameter. The multi-instance manager in
turn executes postfix(1) commands for the default instance and for
all Postfix instances in $multi_instance_directories.

Currently, this parameter setting is ignored except for the
default main.cf file.

This feature is available in Postfix 2.6 and later.


(default: no)

Allow this Postfix instance to be started, stopped, etc., by a
multi-instance manager. By default, new instances are created in
a safe state that prevents them from being started inadvertently.
This parameter is reserved for the multi-instance manager.

This feature is available in Postfix 2.6 and later.


(default: empty)

The optional instance group name of this Postfix instance. A
group identifies closely-related Postfix instances that the
multi-instance manager can start, stop, etc., as a unit. This
parameter is reserved for the multi-instance manager.

This feature is available in Postfix 2.6 and later.


(default: empty)

The optional instance name of this Postfix instance. This name
becomes also the default value for the syslog_name parameter.

This feature is available in Postfix 2.6 and later.


(default: empty)

The pathname of a multi-instance manager command that the
postfix(1) command invokes when the multi_instance_directories
parameter value is non-empty. The pathname may be followed by
initial command arguments separated by whitespace; shell
metacharacters such as quotes are not supported in this context.

The postfix(1) command invokes the manager command with the
postfix(1) non-option command arguments on the manager command line,
and with all installation configuration parameters exported into
the manager command process environment. The manager command in
turn invokes the postfix(1) command for individual Postfix instances
as “postfix -c config_directorycommand“.

This feature is available in Postfix 2.6 and later.


(default: 550)

The numerical Postfix SMTP server response code when a remote SMTP
client request is blocked by the reject_multi_recipient_bounce
restriction.

Do not change this unless you have a complete understanding of RFC 5321.

This feature is available in Postfix 2.1 and later.


(default: $myhostname, localhost.$mydomain, localhost)

The list of domains that are delivered via the $local_transport
mail delivery transport. By default this is the Postfix local(8)
delivery agent which looks up all recipients in /etc/passwd and
/etc/aliases. The SMTP server validates recipient addresses with
$local_recipient_maps and rejects non-existent recipients. See also
the local domain class in the ADDRESS_CLASS_README file.

The default mydestination value specifies names for the local
machine only. On a mail domain gateway, you should also include
$mydomain.

The $local_transport delivery method is also selected for mail
addressed to user@[the.net.work.address] of the mail system (the
IP addresses specified with the inet_interfaces and proxy_interfaces
parameters).

Warnings:

Specify a list of host or domain names, “/file/name” or “type:table
patterns, separated by commas and/or whitespace. A “/file/name”
pattern is replaced by its contents; a “type:table” lookup table
is matched when a name matches a lookup key (the lookup result is
ignored). Continue long lines by starting the next line with
whitespace.

Examples:

mydestination = $myhostname, localhost.$mydomain $mydomainmydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

(default: see “postconf -d” output)

The internet domain name of this mail system. The default is to
use $myhostname minus the first component, or “localdomain” (Postfix
2.3 and later). $mydomain is used as
a default value for many other configuration parameters.

Example:

mydomain = domain.tld

(default: see “postconf -d” output)

The internet hostname of this mail system. The default is to use
the fully-qualified domain name (FQDN) from gethostname(), or to
use the non-FQDN result from gethostname() and append “.$mydomain“.
$myhostname is used as a default value for many other configuration
parameters.

Example:

myhostname = host.example.com

(default: see “postconf -d” output)

The list of “trusted” remote SMTP clients that have more privileges than
“strangers”.

In particular, “trusted” SMTP clients are allowed to relay mail
through Postfix. See the smtpd_relay_restrictions parameter
description in the postconf(5) manual.

You can specify the list of “trusted” network addresses by hand
or you can let Postfix do it for you (which is the default).
See the description of the mynetworks_style parameter for more
information.

If you specify the mynetworks list by hand,
Postfix ignores the mynetworks_style setting.

Specify a list of network addresses or network/netmask patterns,
separated by commas and/or whitespace. Continue long lines by
starting the next line with whitespace.

The netmask specifies the number of bits in the network part
of a host address. You can also specify “/file/name” or “type:table
patterns. A “/file/name” pattern is replaced by its contents; a
type:table” lookup table is matched when a table entry matches a
lookup string (the lookup result is ignored).

The list is matched left to right, and the search stops on the
first match. Specify “!pattern” to exclude an address or network
block from the list. The form “!/file/name” is supported only
in Postfix version 2.4 and later.

Note 1: Pattern matching of domain names is controlled by the
presence or absence of “mynetworks” in the parent_domain_matches_subdomains
parameter value.

Note 2: IP version 6 address information must be specified inside
[] in the mynetworks value, and in files specified with
“/file/name”. IP version 6 addresses contain the “:” character,
and would otherwise be confused with a “type:table” pattern.

Note 3: CIDR ranges cannot be specified in hash tables. Use cidr
tables if CIDR ranges are used.

Examples:

mynetworks = 127.0.0.0/8 168.100.189.0/28
mynetworks = !192.168.0.1, 192.168.0.0/28
mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
mynetworks = $config_directory/mynetworks
mynetworks = hash:/etc/postfix/network_table
mynetworks = cidr:/etc/postfix/network_table.cidr

(default: Postfix ≥ 3.0: host, Postfix < 3.0: subnet)

The method to generate the default value for the mynetworks parameter.
This is the list of trusted networks for relay access control etc.


(default: $myhostname)

The domain name that locally-posted mail appears to come
from, and that locally posted mail is delivered to. The default,
$myhostname, is adequate for small sites. If you run a domain with
multiple machines, you should (1) change this to $mydomain and (2)
set up a domain-wide alias database that aliases each user to
user@that.users.mailhost.

Example:

myorigin = $mydomain

(default: $header_checks)

Optional lookup tables for content inspection of non-MIME message
headers in attached messages, as described in the header_checks(5)
manual page.

This feature is available in Postfix 2.0 and later.


(default: see “postconf -d” output)

Sendmail compatibility feature that specifies the location of the
newaliases(1) command. This command can be used to rebuild the
local(8)aliases(5) database.


(default: 504)

The numerical Postfix SMTP server reply code when a client request
is rejected by the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender
or reject_non_fqdn_recipient restriction.


(default: empty)

A list of Milter (mail filter) applications for new mail that
does not arrive via the Postfix smtpd(8) server. This includes local
submission via the sendmail(1) command line, new mail that arrives
via the Postfix qmqpd(8) server, and old mail that is re-injected
into the queue with “postsuper -r”. Specify space or comma as a
separator. See the MILTER_README document for details.

This feature is available in Postfix 2.3 and later.


(default: resource, software)

The list of error classes that are reported to the postmaster. These
postmaster notifications do not replace user notifications. The
default is to report only the most serious problems. The paranoid
may wish to turn on the policy (UCE and mail relaying) and protocol
error (broken mail software) reports.

NOTE: postmaster notifications may contain confidential information
such as SASL passwords or message content. It is the system
administrator’s responsibility to treat such information with care.

The error classes are:

bounce (also implies 2bounce)
Send the postmaster copies of the headers of bounced mail, and
send transcripts of SMTP sessions when Postfix rejects mail. The
notification is sent to the address specified with the
bounce_notice_recipient configuration parameter (default: postmaster).
2bounce
Send undeliverable bounced mail to the postmaster. The notification
is sent to the address specified with the 2bounce_notice_recipient
configuration parameter (default: postmaster).
data
Send the postmaster a transcript of the SMTP session with an
error because a critical data file was unavailable. The notification
is sent to the address specified with the error_notice_recipient
configuration parameter (default: postmaster).
This feature
is available in Postfix 2.9 and later.
delay
Send the postmaster copies of the headers of delayed mail (see
delay_warning_time). The
notification is sent to the address specified with the
delay_notice_recipient configuration parameter (default: postmaster).
policy
Send the postmaster a transcript of the SMTP session when a
client request was rejected because of (UCE) policy. The notification
is sent to the address specified with the error_notice_recipient
configuration parameter (default: postmaster).
protocol
Send the postmaster a transcript of the SMTP session in case
of client or server protocol errors. The notification is sent to
the address specified with the error_notice_recipient configuration
parameter (default: postmaster).
resource
Inform the postmaster of mail not delivered due to resource
problems. The notification is sent to the address specified with
the error_notice_recipient configuration parameter (default:
postmaster).
software
Inform the postmaster of mail not delivered due to software
problems. The notification is sent to the address specified with
the error_notice_recipient configuration parameter (default:
postmaster).

Examples:

notify_classes = bounce, delay, policy, protocol, resource, software
notify_classes = 2bounce, resource, software

(default: openssl)

The location of the OpenSSL command line program openssl(1). This
is used by the “postfix tls” command to create private keys,
certificate signing requests, self-signed certificates, and to
compute public key digests for DANE TLSA records. In multi-instance
environments, this parameter is always determined from the configuration
of the default Postfix instance.

Example:

/etc/postfix/main.cf:
    # NetBSD pkgsrc:
    openssl_path = /usr/pkg/bin/openssl
    # Local build:
    openssl_path = /usr/local/bin/openssl

This feature is available in Postfix 3.1 and later.


(default: yes)

Enable special treatment for owner-listname entries in the
aliases(5) file, and don’t split owner-listname and
listname-request address localparts when the recipient_delimiter
is set to “-“. This feature is useful for mailing lists.


(default: see “postconf -d” output)

A list of Postfix features where the pattern “example.com” also
matches subdomains of example.com,
instead of requiring an explicit “.example.com” pattern. This is
planned backwards compatibility: eventually, all Postfix features
are expected to require explicit “.example.com” style patterns when
you really want to match subdomains.

The following Postfix feature names are supported.

Postfix version 1.0 and later
debug_peer_list,
fast_flush_domains,
mynetworks,
permit_mx_backup_networks,
relay_domains,
transport_maps
Postfix version 1.1 and later
qmqpd_authorized_clients,
smtpd_access_maps,
Postfix version 2.8 and later
postscreen_access_list
Postfix version 3.0 and later
smtpd_client_event_limit_exceptions

(default: empty)

Restrict the use of the permit_mx_backup SMTP access feature to
only domains whose primary MX hosts match the listed networks.
The parameter value syntax is the same as with the mynetworks
parameter; note, however, that the default value is empty.

Pattern matching of domain names is controlled by the presence
or absence of “permit_mx_backup_networks” in the
parent_domain_matches_subdomains parameter value.


(default: pickup)

The name of the pickup(8) service. This service picks up local mail
submissions from the Postfix maildrop queue.

This feature is available in Postfix 2.0 and later.


(default: $default_delivery_status_filter)

Optional filter for the pipe(8) delivery agent to change the
delivery status code or explanatory text of successful or unsuccessful
deliveries. See default_delivery_status_filter for details.

This feature is available in Postfix 3.0 and later.


(default: 450)

The numerical Postfix SMTP server response code when a request
is rejected by the reject_plaintext_session restriction.

This feature is available in Postfix 2.3 and later.


(default: postlog)

The name of the postlogd(8) service entry in master.cf.
This service appends logfile records to the file specified
with the maillog_file parameter.

This feature is available in Postfix 3.4 and later.


(default: 10s)

How much time a postlogd(8) process may take to process a request
before it is terminated by a built-in watchdog timer. This is a
safety mechanism that prevents postlogd(8) from becoming non-responsive
due to a bug in Postfix itself or in system software. This limit
cannot be set under 10s.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 3.4 and later.


(default: reload flush)

The postfix(1) commands that the postmulti(1) instance manager
treats as “control” commands, that operate on running instances. For
these commands, disabled instances are skipped.

This feature is available in Postfix 2.6 and later.


(default: start)

The postfix(1) commands that the postmulti(1) instance manager treats
as “start” commands. For these commands, disabled instances are “checked”
rather than “started”, and failure to “start” a member instance of an
instance group will abort the start-up of later instances.

This feature is available in Postfix 2.6 and later.


(default: see “postconf -d” output)

The postfix(1) commands that the postmulti(1) instance manager treats
as “stop” commands. For these commands, disabled instances are skipped,
and enabled instances are processed in reverse order.

This feature is available in Postfix 2.6 and later.


(default: permit_mynetworks)

Permanent allow/denylist for remote SMTP client IP addresses.
postscreen(8) searches this list immediately after a remote SMTP
client connects. Specify a comma- or whitespace-separated list of
commands (in upper or lower case) or lookup tables. The search stops
upon the first command that fires for the client IP address.

permit_mynetworks
Allowlist the client and
terminate the search if the client IP address matches $mynetworks.
Do not subject the client to any before/after 220 greeting tests.
Pass the connection immediately to a Postfix SMTP server process.

Pattern matching of domain names is controlled by the presence
or absence of “postscreen_access_list” in the
parent_domain_matches_subdomains parameter value.
type:table
Query the specified lookup
table. Each table lookup result is an access list, except that
access lists inside a table cannot specify type:table entries.
To discourage the use of hash, btree, etc. tables, there is no
support for substring matching like smtpd(8). Use CIDR tables
instead.
permit
Allowlist the client and terminate
the search. Do not subject the client to any before/after 220
greeting tests. Pass the connection immediately to a Postfix SMTP
server process.
reject
Denylist the client and terminate
the search. Subject the client to the action configured with the
postscreen_denylist_action configuration parameter.
dunno
All postscreen(8) access lists
implicitly have this command at the end.
When dunno
is executed inside a lookup table, return from the lookup table and
evaluate the next command.
When dunno is executed
outside a lookup table, terminate the search, and subject the client
to the configured before/after 220 greeting tests.

Example:

/etc/postfix/main.cf:
    postscreen_access_list = permit_mynetworks,
        cidr:/etc/postfix/postscreen_access.cidr
    # Postfix < 3.6 use postscreen_blacklist_action.
    postscreen_denylist_action = enforce
/etc/postfix/postscreen_access.cidr:
    # Rules are evaluated in the order as specified.
    # Denylist 192.168.* except 192.168.0.1.
    192.168.0.1         dunno
    192.168.0.0/16      reject

This feature is available in Postfix 2.8.


(default: static:all)

A list of local postscreen(8) server IP addresses where a
non-allowlisted remote SMTP client can obtain postscreen(8)‘s temporary
allowlist status. This status is required before the client can
talk to a Postfix SMTP server process. By default, a client can
obtain postscreen(8)‘s allowlist status on any local postscreen(8)
server IP address.

When postscreen(8) listens on both primary and backup MX
addresses, the postscreen_allowlist_interfaces parameter can be
configured to give the temporary allowlist status only when a client
connects to a primary MX address. Once a client is allowlisted it
can talk to a Postfix SMTP server on any address. Thus, clients
that connect only to backup MX addresses will never become allowlisted,
and will never be allowed to talk to a Postfix SMTP server process.

Specify a list of network addresses or network/netmask patterns,
separated by commas and/or whitespace. The netmask specifies the
number of bits in the network part of a host address. Continue long
lines by starting the next line with whitespace.

You can also specify “/file/name” or “type:table” patterns. A
“/file/name” pattern is replaced by its contents; a “type:table
lookup table is matched when a table entry matches a lookup string
(the lookup result is ignored).

The list is matched left to right, and the search stops on the
first match. Specify “!pattern” to exclude an address or network
block from the list.

Note: IP version 6 address information must be specified inside
[] in the postscreen_allowlist_interfaces value, and in files
specified with “/file/name”. IP version 6 addresses contain the
“:” character, and would otherwise be confused with a “type:table
pattern.

Example:

/etc/postfix/main.cf:
    # Don't allowlist connections to the backup IP address.
    # Postfix < 3.6 use postscreen_whitelist_interfaces.
    postscreen_allowlist_interfaces = !168.100.189.8, static:all

This feature is available in Postfix 3.6 and later.

Available as postscreen_whitelist_interfaces in Postfix 2.9 – 3.5.


(default: ignore)

The action that postscreen(8) takes when a remote SMTP client sends
a bare newline character, that is, a newline not preceded by carriage
return. Specify one of the following:

ignore
Ignore the failure of this test. Allow other tests to complete.
Do not repeat this test before the result from some
other test expires.
This option is useful for testing and collecting statistics
without blocking mail permanently.
enforce
Allow other tests to complete. Reject attempts to deliver mail
with a 550 SMTP reply, and log the helo/sender/recipient information.
Repeat this test the next time the client connects.
drop
Drop the connection immediately with a 521 SMTP reply. Repeat
this test the next time the client connects.

This feature is available in Postfix 2.8.


(default: no)

Enable “bare newline” SMTP protocol tests in the postscreen(8)
server. These tests are expensive: a remote SMTP client must
disconnect after
it passes the test, before it can talk to a real Postfix SMTP server.

This feature is available in Postfix 2.8.


(default: 30d)

The amount of time that postscreen(8) will use the result from
a successful “bare newline” SMTP protocol test. During this
time, the client IP address is excluded from this test. The default
is long because a remote SMTP client must disconnect after it passes
the test,
before it can talk to a real Postfix SMTP server.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.8.


(default: ignore)

Renamed to postscreen_denylist_action in Postfix 3.6.

This feature is available in Postfix 2.8 – 3.5.


(default: 12h)

The amount of time between postscreen(8) cache cleanup runs.
Cache cleanup increases the load on the cache database and should
therefore not be run frequently. This feature requires that the
cache database supports the “delete” and “sequence” operators.
Specify a zero interval to disable cache cleanup.

After each cache cleanup run, the postscreen(8) daemon logs the
number of entries that were retained and dropped. A cleanup run is
logged as “partial” when the daemon terminates early after “postfix
reload
“, “postfix stop“, or no requests for $max_idle
seconds.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).

This feature is available in Postfix 2.8.


(default: btree:$data_directory/postscreen_cache)

Persistent storage for the postscreen(8) server decisions.

To share a postscreen(8) cache between multiple postscreen(8)
instances, use “postscreen_cache_map = proxy:btree:/path/to/file”.
This requires Postfix version 2.9 or later; earlier proxymap(8)
implementations don’t support cache cleanup. For an alternative
approach see the memcache_table(5) manpage.

This feature is available in Postfix 2.8.


(default: 7d)

The amount of time that postscreen(8) will cache an expired
temporary allowlist entry before it is removed. This prevents clients
from being logged as “NEW” just because their cache entry expired
an hour ago. It also prevents the cache from filling up with clients
that passed some deep protocol test once and never came back.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.8.


(default: $smtpd_client_connection_count_limit)

How many simultaneous connections any remote SMTP client is
allowed to have
with the postscreen(8) daemon. By default, this limit is the same
as with the Postfix SMTP server. Note that the triage process can
take several seconds, with the time spent in postscreen_greet_wait
delay, and with the time spent talking to the postscreen(8) built-in
dummy SMTP protocol engine.

This feature is available in Postfix 2.8.


(default: 20)

The limit on the total number of commands per SMTP session for
postscreen(8)‘s built-in SMTP protocol engine. This SMTP engine
defers or rejects all attempts to deliver mail, therefore there is
no need to enforce separate limits on the number of junk commands
and error commands.

This feature is available in Postfix 2.8.


(default: $smtpd_command_filter)

A mechanism to transform commands from remote SMTP clients.
See smtpd_command_filter for further details.

This feature is available in Postfix 2.8 and later.


(default: normal: 300s, overload: 10s)

The time limit to read an entire command line with postscreen(8)‘s
built-in SMTP protocol engine.

This feature is available in Postfix 2.8.


(default: ignore)

The action that postscreen(8) takes when a remote SMTP client is
permanently denylisted with the postscreen_access_list parameter.
Specify one of the following:

ignore (default)
Ignore this result. Allow other tests to complete. Repeat
this test the next time the client connects.
This option is useful for testing and collecting statistics
without blocking mail.
enforce
Allow other tests to complete. Reject attempts to deliver mail
with a 550 SMTP reply, and log the helo/sender/recipient information.
Repeat this test the next time the client connects.
drop
Drop the connection immediately with a 521 SMTP reply. Repeat
this test the next time the client connects.

This feature is available in Postfix 3.6 and later.

Available as postscreen_blacklist_action in Postfix 2.8 – 3.5.


(default: $disable_vrfy_command)

Disable the SMTP VRFY command in the postscreen(8) daemon. See
disable_vrfy_command for details.

This feature is available in Postfix 2.8.


(default: $smtpd_discard_ehlo_keyword_address_maps)

Lookup tables, indexed by the remote SMTP client address, with
case insensitive lists of EHLO keywords (pipelining, starttls, auth,
etc.) that the postscreen(8) server will not send in the EHLO response
to a remote SMTP client. See smtpd_discard_ehlo_keywords for details.
The table is not searched by hostname for robustness reasons.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_discard_ehlo_keywords)

A case insensitive list of EHLO keywords (pipelining, starttls,
auth, etc.) that the postscreen(8) server will not send in the EHLO
response to a remote SMTP client. See smtpd_discard_ehlo_keywords
for details.

This feature is available in Postfix 2.8 and later.


(default: ignore)

The action that postscreen(8) takes when a remote SMTP client’s combined
DNSBL score is equal to or greater than a threshold (as defined
with the postscreen_dnsbl_sites and postscreen_dnsbl_threshold
parameters). Specify one of the following:

ignore (default)
Ignore the failure of this test. Allow other tests to complete.
Repeat this test the next time the client connects.
This option is useful for testing and collecting statistics
without blocking mail.
enforce
Allow other tests to complete. Reject attempts to deliver mail
with a 550 SMTP reply, and log the helo/sender/recipient information.
Repeat this test the next time the client connects.
drop
Drop the connection immediately with a 521 SMTP reply. Repeat
this test the next time the client connects.

This feature is available in Postfix 2.8.


(default: 0)

Allow a remote SMTP client to skip “before” and “after 220
greeting” protocol tests, based on its combined DNSBL score as
defined with the postscreen_dnsbl_sites parameter.

Specify a negative value to enable this feature. When a client
passes the postscreen_dnsbl_allowlist_threshold without having
failed other tests, all pending or disabled tests are flagged as
completed with a time-to-live value equal to postscreen_dnsbl_ttl.
When a test was already completed, its time-to-live value is updated
if it was less than postscreen_dnsbl_ttl.

This feature is available in Postfix 3.6 and later.

Available as postscreen_dnsbl_whitelist_threshold in Postfix 2.11
– 3.5.


(default: ${postscreen_dnsbl_ttl?{$postscreen_dnsbl_ttl}:{1}}h)

The maximum amount of time that postscreen(8) will use the
result from a successful DNS-based reputation test before a
client IP address is required to pass that test again. If the DNS
reply specifies a shorter TTL value, that value will be used unless
it would be smaller than postscreen_dnsbl_min_ttl.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).

This feature is available in Postfix 3.1. The default setting
is backwards-compatible with older Postfix versions.


(default: 60s)

The minimum amount of time that postscreen(8) will use the
result from a successful DNS-based reputation test before a
client IP address is required to pass that test again. If the DNS
reply specifies a larger TTL value, that value will be used unless
it would be larger than postscreen_dnsbl_max_ttl.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 3.1.


(default: empty)

A mapping from an actual DNSBL domain name which includes a secret
password, to the DNSBL domain name that postscreen will reply with
when it rejects mail. When no mapping is found, the actual DNSBL
domain will be used.

For maximal stability it is best to use a file that is read
into memory such as pcre:, regexp: or texthash: (texthash: is similar
to hash:, except a) there is no need to run postmap(1) before the
file can be used, and b) texthash: does not detect changes after
the file is read).

Example:

/etc/postfix/main.cf:
    postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply
/etc/postfix/dnsbl_reply:
   secret.zen.spamhaus.org      zen.spamhaus.org

This feature is available in Postfix 2.8.


(default: empty)

Optional list of DNS allow/denylist domains, filters and weight
factors. When the list is non-empty, the dnsblog(8) daemon will
query these domains with the IP addresses of remote SMTP clients,
and postscreen(8) will update an SMTP client’s DNSBL score with
each non-error reply.

Caution: when postscreen rejects mail, it replies with the DNSBL
domain name. Use the postscreen_dnsbl_reply_map feature to hide
“password” information in DNSBL domain names.

When a client’s score is equal to or greater than the threshold
specified with postscreen_dnsbl_threshold, postscreen(8) can drop
the connection with the remote SMTP client.

Specify a list of domain=filter*weight entries, separated by
comma or whitespace.

Examples:

To use example.com as a high-confidence blocklist, and to
block mail with example.net and example.org only when both agree:

postscreen_dnsbl_threshold = 2
postscreen_dnsbl_sites = example.com*2, example.net, example.org

To filter only DNSBL replies containing 127.0.0.4:

postscreen_dnsbl_sites = example.com=127.0.0.4

This feature is available in Postfix 2.8.


(default: 1)

The inclusive lower bound for blocking a remote SMTP client, based on
its combined DNSBL score as defined with the postscreen_dnsbl_sites
parameter.

This feature is available in Postfix 2.8.


(default: 10s)

The time limit for DNSBL or DNSWL lookups. This is separate from
the timeouts in the dnsblog(8) daemon which are defined by system
resolver(3) routines.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 3.0.


(default: 1h)

The amount of time that postscreen(8) will use the result from
a successful DNS-based reputation test before a client
IP address is required to pass that test again.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).

This feature is available in Postfix 2.8-3.0. It was
replaced by postscreen_dnsbl_max_ttl in Postfix 3.1.


(default: 0)

Renamed to postscreen_dnsbl_allowlist_threshold in Postfix 3.6.

This feature is available in Postfix 2.11 – 3.5.


(default: $smtpd_enforce_tls)

Mandatory TLS: announce STARTTLS support to remote SMTP clients, and
require that clients use TLS encryption. See smtpd_postscreen_enforce_tls
for details.

This feature is available in Postfix 2.8 and later.
Preferably, use postscreen_tls_security_level instead.


(default: see “postconf -d” output)

List of characters that are permitted in postscreen_reject_footer
attribute expansions. See smtpd_expansion_filter for further
details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_forbidden_commands)

List of commands that the postscreen(8) server considers in
violation of the SMTP protocol. See smtpd_forbidden_commands for
syntax, and postscreen_non_smtp_command_action for possible actions.

This feature is available in Postfix 2.8.


(default: ignore)

The action that postscreen(8) takes when a remote SMTP client speaks
before its turn within the time specified with the postscreen_greet_wait
parameter. Specify one of the following:

ignore (default)
Ignore the failure of this test. Allow other tests to complete.
Repeat this test the next time the client connects.
This option is useful for testing and collecting statistics
without blocking mail.
enforce
Allow other tests to complete. Reject attempts to deliver mail
with a 550 SMTP reply, and log the helo/sender/recipient information.
Repeat this test the next time the client connects.
drop
Drop the connection immediately with a 521 SMTP reply. Repeat
this test the next time the client connects.

In either case, postscreen(8) will not allowlist the remote SMTP client
IP address.

This feature is available in Postfix 2.8.


(default: $smtpd_banner)

The text in the optional “220-text…” server
response that
postscreen(8) sends ahead of the real Postfix SMTP server’s “220
text…” response, in an attempt to confuse bad SMTP clients so
that they speak before their turn (pre-greet). Specify an empty
value to disable this feature.

This feature is available in Postfix 2.8.


(default: 1d)

The amount of time that postscreen(8) will use the result from
a successful PREGREET test. During this time, the client IP address
is excluded from this test. The default is relatively short, because
a good client can immediately talk to a real Postfix SMTP server.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.8.


(default: normal: 6s, overload: 2s)

The amount of time that postscreen(8) will wait for an SMTP
client to send a command before its turn, and for DNS blocklist
lookup results to arrive (default: up to 2 seconds under stress,
up to 6 seconds otherwise).

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.8.


(default: $smtpd_helo_required)

Require that a remote SMTP client sends HELO or EHLO before
commencing a MAIL transaction.

This feature is available in Postfix 2.8.


(default: drop)

The action that postscreen(8) takes when a remote SMTP client sends
non-SMTP commands as specified with the postscreen_forbidden_commands
parameter. Specify one of the following:

ignore
Ignore the failure of this test. Allow other tests to complete.
Do not repeat this test before the result from some
other test expires.
This option is useful for testing and collecting statistics
without blocking mail permanently.
enforce
Allow other tests to complete. Reject attempts to deliver mail
with a 550 SMTP reply, and log the helo/sender/recipient information.
Repeat this test the next time the client connects.
drop
Drop the connection immediately with a 521 SMTP reply. Repeat
this test the next time the client connects. This action is the
same as with the Postfix SMTP server’s smtpd_forbidden_commands
feature.

This feature is available in Postfix 2.8.


(default: no)

Enable “non-SMTP command” tests in the postscreen(8) server. These
tests are expensive: a client must disconnect after it passes the
test, before it can talk to a real Postfix SMTP server.

This feature is available in Postfix 2.8.


(default: 30d)

The amount of time that postscreen(8) will use the result from
a successful “non_smtp_command” SMTP protocol test. During this
time, the client IP address is excluded from this test. The default
is long because a client must disconnect after it passes the test,
before it can talk to a real Postfix SMTP server.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.8.


(default: enforce)

The action that postscreen(8) takes when a remote SMTP client
sends
multiple commands instead of sending one command and waiting for
the server to respond. Specify one of the following:

ignore
Ignore the failure of this test. Allow other tests to complete.
Do not repeat this test before the result from some
other test expires.
This option is useful for testing and collecting statistics
without blocking mail permanently.
enforce
Allow other tests to complete. Reject attempts to deliver mail
with a 550 SMTP reply, and log the helo/sender/recipient information.
Repeat this test the next time the client connects.
drop
Drop the connection immediately with a 521 SMTP reply. Repeat
this test the next time the client connects.

This feature is available in Postfix 2.8.


(default: no)

Enable “pipelining” SMTP protocol tests in the postscreen(8)
server. These tests are expensive: a good client must disconnect
after it passes the test, before it can talk to a real Postfix SMTP
server.

This feature is available in Postfix 2.8.


(default: 30d)

The amount of time that postscreen(8) will use the result from
a successful “pipelining” SMTP protocol test. During this time, the
client IP address is excluded from this test. The default is
long because a good client must disconnect after it passes the test,
before it can talk to a real Postfix SMTP server.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.8.


(default: $default_process_limit)

The number of clients that can be waiting for service from a
real Postfix SMTP server process. When this queue is full, all
clients will
receive a 421 response.

This feature is available in Postfix 2.8.


(default: $default_process_limit)

The number of non-allowlisted clients that can be waiting for
a decision whether they will receive service from a real Postfix
SMTP server
process. When this queue is full, all non-allowlisted clients will
receive a 421 response.

This feature is available in Postfix 2.8.


(default: $smtpd_reject_footer)

Optional information that is appended after a 4XX or 5XX
postscreen(8) server
response. See smtpd_reject_footer for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_reject_footer_maps)

Optional lookup table for information that is appended after a 4XX
or 5XX postscreen(8) server response. See smtpd_reject_footer_maps for
further details.

This feature is available in Postfix 3.4 and later.


(default: $smtpd_tls_security_level)

The SMTP TLS security level for the postscreen(8) server; when
a non-empty value is specified, this overrides the obsolete parameters
postscreen_use_tls and postscreen_enforce_tls. See smtpd_tls_security_level
for details.

This feature is available in Postfix 2.8 and later.


(default: empty)

The name of the proxy protocol used by an optional before-postscreen
proxy agent. When a proxy agent is used, this protocol conveys local
and remote address and port information. Specify
postscreen_upstream_proxy_protocol = haproxy” to enable the haproxy
protocol; version 2 is supported with Postfix 3.5 and later.

This feature is available in Postfix 2.10 and later.


(default: 5s)

The time limit for the proxy protocol specified with the
postscreen_upstream_proxy_protocol parameter.

This feature is available in Postfix 2.10 and later.


(default: $smtpd_use_tls)

Opportunistic TLS: announce STARTTLS support to remote SMTP clients,
but do not require that clients use TLS encryption.

This feature is available in Postfix 2.8 and later.
Preferably, use postscreen_tls_security_level instead.


(default: 10s)

How much time a postscreen(8) process may take to respond to
a remote SMTP client command or to perform a cache operation before it
is terminated by a built-in watchdog timer. This is a safety
mechanism that prevents postscreen(8) from becoming non-responsive
due to a bug in Postfix itself or in system software. To avoid
false alarms and unnecessary cache corruption this limit cannot be
set under 10s.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.8.


(default: static:all)

Renamed to postscreen_allowlist_interfaces in Postfix 3.6.

This feature is available in Postfix 2.9 – 3.5.


(default: command, file, forward)

The message delivery contexts where the Postfix local(8) delivery
agent prepends a Delivered-To: message header with the address
that the mail was delivered to. This information is used for mail
delivery loop detection.

By default, the Postfix local delivery agent prepends a Delivered-To:
header when forwarding mail and when delivering to file (mailbox)
and command. Turning off the Delivered-To: header when forwarding
mail is not recommended.

Specify zero or more of forward, file, or command.

Example:

prepend_delivered_header = forward

(read-only)

The process ID of a Postfix command or daemon process.


(default: pid)

The location of Postfix PID files relative to $queue_directory.
This is a read-only parameter.


(read-only)

The process name of a Postfix command or daemon process.


(default: canonical, virtual)

What address lookup tables copy an address extension from the lookup
key to the lookup result.

For example, with a virtual(5) mapping of “joe@example.com =>
joe.user@example.net
“, the address “joe foo@example.com
would rewrite to “joe.user foo@example.net“.

Specify zero or more of canonical, virtual, alias,
forward, include or generic. These cause
address extension
propagation with canonical(5), virtual(5), and aliases(5) maps,
with local(8) .forward and :include: file lookups, and with smtp(8)
generic maps, respectively.

Note: enabling this feature for types other than canonical
and virtual is likely to cause problems when mail is forwarded
to other sites, especially with mail that is sent to a mailing list
exploder address.

Examples:

propagate_unmatched_extensions = canonical, virtual, alias,
        forward, include
propagate_unmatched_extensions = canonical, virtual

(default: empty)

The remote network interface addresses that this mail system receives mail
on by way of a proxy or network address translation unit.

This feature is available in Postfix 2.0 and later.

You must specify your “outside” proxy/NAT addresses when your
system is a backup MX host for other domains, otherwise mail delivery
loops will happen when the primary MX host is down.

Example:

proxy_interfaces = 1.2.3.4

(default: see “postconf -d” output)

The lookup tables that the proxymap(8) server is allowed to
access for the read-only service.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma.
Table references that don’t begin with proxy: are ignored.

This feature is available in Postfix 2.0 and later.


(default: see “postconf -d” output)

The lookup tables that the proxymap(8) server is allowed to
access for the read-write service. Postfix-owned local database
files should be stored under the Postfix-owned data_directory.
Table references that don’t begin with proxy: are ignored.

This feature is available in Postfix 2.5 and later.


(default: proxymap)

The name of the proxymap read-only table lookup service. This
service is normally implemented by the proxymap(8) daemon.

This feature is available in Postfix 2.6 and later.


(default: proxywrite)

The name of the proxywrite read-write table lookup service.
This service is normally implemented by the proxymap(8) daemon.

This feature is available in Postfix 2.6 and later.


(default: 300s)

The minimal delay between warnings that a specific destination is
clogging up the Postfix active queue. Specify 0 to disable.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is enabled with the helpful_warnings parameter.

This feature is available in Postfix 2.0 and later.


(default: 1000s)

How much time a Postfix queue manager process may take to handle
a request before it is terminated by a built-in watchdog timer.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.8 and later.


(default: 100)

Obsolete feature: the percentage of delivery resources that a busy
mail system will use up for delivery of a large mailing list
message.

This feature exists only in the oqmgr(8) old queue manager. The
current queue manager solves the problem in a better way.


(default: 60s)

The time limit for the queue manager to send or receive information
over an internal communication channel. The purpose is to break
out of deadlock situations. If the time limit is exceeded the
software either retries or aborts the operation.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.8 and later.


(default: 20000)

The maximal number of messages in the active queue.


(default: 20000)

The maximal number of recipients held in memory by the Postfix
queue manager, and the maximal size of the short-term,
in-memory “dead” destination status cache.


(default: 10)

The minimal number of in-memory recipients for any message. This
takes priority over any other in-memory recipient limits (i.e.,
the global qmgr_message_recipient_limit and the per transport
_recipient_limit) if necessary. The minimum value allowed for this
parameter is 1.


(default: empty)

What remote QMQP clients are allowed to connect to the Postfix QMQP
server port.

By default, no client is allowed to use the service. This is
because the QMQP server will relay mail to any destination.

Specify a list of client patterns. A list pattern specifies a host
name, a domain name, an internet address, or a network/mask pattern,
where the mask specifies the number of bits in the network part.
When a pattern specifies a file name, its contents are substituted
for the file name; when a pattern is a “type:table” table specification,
table lookup is used instead.

Patterns are separated by whitespace and/or commas. In order to
reverse the result, precede a pattern with an
exclamation point (!). The form “!/file/name” is supported only
in Postfix version 2.4 and later.

Pattern matching of domain names is controlled by the presence
or absence of “qmqpd_authorized_clients” in the
parent_domain_matches_subdomains parameter value.

Example:

qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

(default: no)

Enable logging of the remote QMQP client port in addition to
the hostname and IP address. The logging format is “host[address]:port”.

This feature is available in Postfix 2.5 and later.


(default: 1s)

How long the Postfix QMQP server will pause before sending a negative
reply to the remote QMQP client. The purpose is to slow down confused
or malicious clients.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 300s)

The time limit for sending or receiving information over the network.
If a read or write operation blocks for more than $qmqpd_timeout
seconds the Postfix QMQP server gives up and disconnects.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: see “postconf -d” output)

The location of the Postfix top-level queue directory. This is the
root directory of Postfix daemon processes that run chrooted.


(default: 100)

The maximal number of (name=value) attributes that may be stored
in a Postfix queue file. The limit is enforced by the cleanup(8)
server.

This feature is available in Postfix 2.0 and later.


(default: 0)

The minimal amount of free space in bytes in the queue file system
that is needed to receive mail. This is currently used by the
Postfix SMTP server to decide if it will accept any mail at all.

By default, the Postfix SMTP server rejects MAIL FROM commands when
the amount of free space is less than 1.5*$message_size_limit
(Postfix version 2.1 and later).
To specify a higher minimum free space limit, specify a queue_minfree
value that is at least 1.5*$message_size_limit.

With Postfix versions 2.0 and earlier, a queue_minfree value of
zero means there is no minimum required amount of free space.


(default: 300s)

The time between deferred queue scans by the queue manager;
prior to Postfix 2.4 the default value was 1000s.

This parameter should be set less than or equal to
$minimal_backoff_time. See also $maximal_backoff_time.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: qmgr)

The name of the qmgr(8) service. This service manages the Postfix
queue and schedules delivery requests.

This feature is available in Postfix 2.0 and later.


(default: empty)

Optional lookup tables with RBL response templates. The tables are
indexed by the RBL domain name. By default, Postfix uses the default
template as specified with the default_rbl_reply configuration
parameter. See there for a discussion of the syntax of RBL reply
templates.

This feature is available in Postfix 2.0 and later.


(default: see “postconf -d” output)

The location of Postfix README files that describe how to build,
configure or operate a specific Postfix subsystem or feature.


(default: empty)

Enable or disable recipient validation, built-in content
filtering, or address mapping. Typically, these are specified in
master.cf as command-line arguments for the smtpd(8), qmqpd(8) or
pickup(8) daemons.

Specify zero or more of the following options. The options
override main.cf settings and are either implemented by smtpd(8),
qmqpd(8), or pickup(8) themselves, or they are forwarded to the
cleanup server.

Do not try to reject unknown recipients (SMTP server only).
This is typically specified AFTER an external content filter.
Disable canonical address mapping, virtual alias map expansion,
address masquerading, and automatic BCC (blind carbon-copy)
recipients. This is typically specified BEFORE an external content
filter.
Disable header/body_checks. This is typically specified AFTER
an external content filter.
Disable Milter (mail filter) applications. This is typically
specified AFTER an external content filter.

Note: when the “BEFORE content filter” receive_override_options
setting is specified in the main.cf file, specify the “AFTER content
filter” receive_override_options setting in master.cf (and vice
versa).

Examples:

receive_override_options =
    no_unknown_recipient_checks, no_header_body_checksreceive_override_options = no_address_mappings

This feature is available in Postfix 2.1 and later.


(default: empty)

Optional BCC (blind carbon-copy) address lookup tables, indexed by
recipient address. The BCC address (multiple results are not
supported) is added when mail enters from outside of Postfix.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

The table search order is as follows:

Note: with Postfix 2.3 and later the BCC address is added as if it
was specified with NOTIFY=NONE. The sender will not be notified
when the BCC address is undeliverable, as long as all down-stream
software implements RFC 3461.

Note: with Postfix 2.2 and earlier the sender will unconditionally
be notified when the BCC address is undeliverable.

Note: automatic BCC recipients are produced only for new mail.
To avoid mailer loops, automatic BCC recipients are not generated
after Postfix forwards mail internally, or after Postfix generates
mail itself.

Example:

recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

After a change, run “postmap /etc/postfix/recipient_bcc“.

This feature is available in Postfix 2.1 and later.


(default: envelope_recipient, header_recipient)

What addresses are subject to recipient_canonical_maps address
mapping. By default, recipient_canonical_maps address mapping is
applied to envelope recipient addresses, and to header recipient
addresses.

Specify one or more of: envelope_recipient, header_recipient

This feature is available in Postfix 2.2 and later.


(default: empty)

Optional address mapping lookup tables for envelope and header
recipient addresses.
The table format and lookups are documented in canonical(5).

Note: $recipient_canonical_maps is processed before $canonical_maps.

Example:

recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

(default: empty)

The set of characters that can separate an email address
localpart, user name, or a .forward file name from its extension.
For example, with “recipient_delimiter = “, the software tries
user foo@example.com before trying user@example.com, user foo before
trying user, and .forward foo before trying .forward.

More formally, an email address localpart or user name is
separated from its extension by the first character that matches
the recipient_delimiter set. The delimiter character and extension
may then be used to generate an extended .forward file name. This
implementation recognizes one delimiter character and one extension
per email address localpart or email address. With Postfix 2.10 and
earlier, the recipient_delimiter specifies a single character.

See canonical(5), local(8), relocated(5) and virtual(5) for the
effects of recipient_delimiter on lookups in aliases, canonical,
virtual, and relocated maps, and see the propagate_unmatched_extensions
parameter for propagating an extension from one email address to
another.

When used in command_execution_directory, forward_path, or
luser_relay, ${recipient_delimiter} is replaced with the actual
recipient delimiter that was found in the recipient email address
(Postfix 2.11 and later), or it is replaced with the main.cfrecipient_delimiter parameter value (Postfix 2.10 and earlier).

The recipient_delimiter is not applied to the mailer-daemon
address, the postmaster address, or the double-bounce address. With
the default “owner_request_special = yes” setting, the recipient_delimiter
is also not applied to addresses with the special “owner-” prefix
or the special “-request” suffix.

Examples:

# Handle Postfix-style extensions.
recipient_delimiter =  
# Handle both Postfix and qmail extensions (Postfix 2.11 and later).
recipient_delimiter =  -
# Use .forward for mail without address extension, and for mail with
# an unrecognized address extension.
forward_path = $home/.forward${recipient_delimiter}${extension},
    $home/.forward

(default: 554)

The numerical Postfix SMTP server response code when a remote SMTP
client request is rejected by the “reject” restriction.

Do not change this unless you have a complete understanding of RFC 5321.


(default: defer_if_permit)

The Postfix SMTP server’s action when a reject-type restriction
fails due to a temporary error condition. Specify “defer” to defer
the remote SMTP client request immediately. With the default
defer_if_permit” action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted.

For finer control, see: unverified_recipient_tempfail_action,
unverified_sender_tempfail_action, unknown_address_tempfail_action,
and unknown_helo_hostname_tempfail_action.

This feature is available in Postfix 2.6 and later.


(default: empty)

List of tables with remote SMTP client-certificate fingerprints or
public key fingerprints (Postfix 2.9 and later) for which the Postfix
SMTP server will allow access with the permit_tls_clientcerts
feature. The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5).

The default algorithm is sha256 with Postfix ≥ 3.6
and the compatibility_level set to 3.6 or higher. With Postfix
≤ 3.5, the default algorithm is md5. The best-practice
algorithm is now sha256. Recent advances in hash function
cryptanalysis have led to md5 and sha1 being deprecated in favor of
sha256. However, as long as there are no known “second pre-image”
attacks against the older algorithms, their use in this context, though
not recommended, is still likely safe.

Postfix lookup tables are in the form of (key, value) pairs.
Since we only need the key, the value can be chosen freely, e.g.
the name of the user or host:
D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80 lutzpc.at.home

Example:

relay_clientcerts = hash:/etc/postfix/relay_clientcerts

For more fine-grained control, use check_ccert_access to select
an appropriate access(5) policy for each client.
See RESTRICTION_CLASS_README.

This feature is available with Postfix version 2.2.


(default: $default_destination_concurrency_limit)

The maximal number of parallel deliveries to the same destination
via the relay message delivery transport. This limit is enforced
by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.

This feature is available in Postfix 2.0 and later.


(default: $default_destination_recipient_limit)

The maximal number of recipients per message for the relay
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.

Setting this parameter to a value of 1 changes the meaning of
relay_destination_concurrency_limit from concurrency per domain
into concurrency per recipient.

This feature is available in Postfix 2.0 and later.


(default: Postfix ≥ 3.0: empty, Postfix < 3.0: $mydestination)

What destination domains (and subdomains thereof) this system
will relay mail to. For details about how
the relay_domains value is used, see the description of the
permit_auth_destination and reject_unauth_destination SMTP recipient
restrictions.

Domains that match $relay_domains are delivered with the
$relay_transport mail delivery transport. The SMTP server validates
recipient addresses with $relay_recipient_maps and rejects non-existent
recipients. See also the relay domains address class in the
ADDRESS_CLASS_README file.

Note: Postfix will not automatically forward mail for domains
that list this system as their primary or backup MX host. See the
permit_mx_backup restriction in the postconf(5) manual page.

Specify a list of host or domain names, “/file/name” patterns
or “type:table” lookup tables, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace. A
“/file/name” pattern is replaced by its contents; a “type:table
lookup table is matched when a (parent) domain appears as lookup
key. Specify “!pattern” to exclude a domain from the list. The form
“!/file/name” is supported only in Postfix version 2.4 and later.

Pattern matching of domain names is controlled by the presence
or absence of “relay_domains” in the parent_domain_matches_subdomains
parameter value.


(default: 554)

The numerical Postfix SMTP server response code when a client
request is rejected by the reject_unauth_destination recipient
restriction.

Do not change this unless you have a complete understanding of RFC 5321.


(default: empty)

Optional lookup tables with all valid addresses in the domains
that match $relay_domains. Specify @domain as a wild-card for
domains that have no valid recipient list, and become a source of
backscatter mail: Postfix accepts spam for non-existent recipients
and then floods innocent people with undeliverable mail. Technically,
tables
listed with $relay_recipient_maps are used as lists: Postfix needs
to know only if a lookup string is found or not, but it does not
use the result from the table lookup.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

If this parameter is non-empty, then the Postfix SMTP server will reject
mail to unknown relay users. This feature is off by default.

See also the relay domains address class in the ADDRESS_CLASS_README
file.

Example:

relay_recipient_maps = hash:/etc/postfix/relay_recipients

This feature is available in Postfix 2.0 and later.


(default: relay)

The default mail delivery transport and next-hop destination for
remote delivery to domains listed with $relay_domains. In order of
decreasing precedence, the nexthop destination is taken from
$relay_transport, $sender_dependent_relayhost_maps, $relayhost, or
from the recipient domain. This information can be overruled with
the transport(5) table.

Specify a string of the form transport:nexthop, where transport
is the name of a mail delivery transport defined in master.cf.
The :nexthop destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent.

See also the relay domains address class in the ADDRESS_CLASS_README
file.

This feature is available in Postfix 2.0 and later.


(default: empty)

The next-hop destination(s) for non-local mail; overrides non-local
domains in recipient addresses. This information is overruled with
relay_transport, sender_dependent_default_transport_maps,
default_transport, sender_dependent_relayhost_maps
and with the transport(5) table.

On an intranet, specify the organizational domain name. If your
internal DNS uses no MX records, specify the name of the intranet
gateway host instead.

In the case of SMTP or LMTP delivery, specify one or more destinations
in the form of a domain name, hostname, hostname:port, [hostname]:port,
[hostaddress] or [hostaddress]:port, separated by comma or whitespace.
The form [hostname] turns off MX lookups. Multiple destinations are
supported in Postfix 3.5 and later.

If you’re connected via UUCP, see the UUCP_README file for useful
information.

Examples:

relayhost = $mydomainrelayhost = [gateway.example.com]
relayhost = mail1.example:587, mail2.example:587
relayhost = [an.ip.add.ress]

(default: empty)

Optional lookup tables with new contact information for users or
domains that no longer exist. The table format and lookups are
documented in relocated(5).

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

If you use this feature, run “postmap /etc/postfix/relocated” to
build the necessary DBM or DB file after change, then “postfix
reload
” to make the changes visible.

Examples:

relocated_maps = dbm:/etc/postfix/relocated
relocated_maps = hash:/etc/postfix/relocated

(default: empty)

Don’t rewrite message headers from remote clients at all when
this parameter is empty; otherwise, rewrite message headers and
append the specified domain name to incomplete addresses. The
local_header_rewrite_clients parameter controls what clients Postfix
considers local.

Examples:

The safe setting: append “domain.invalid” to incomplete header
addresses from remote SMTP clients, so that those addresses cannot
be confused with local addresses.

remote_header_rewrite_domain = domain.invalid

The default, purist, setting: don’t rewrite headers from remote
clients at all.

remote_header_rewrite_domain =


(default: no)

Require that a local(8) recipient’s home directory exists
before mail delivery is attempted. By default this test is disabled.
It can be useful for environments that import home directories to
the mail server (IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).


(default: no)

Reset the local(8) delivery agent’s idea of the owner-alias
attribute, when delivering mail to a child alias that does not have
its own owner alias.

This feature is available in Postfix 2.8 and later. With older
Postfix releases, the behavior is as if this parameter is set to
“yes”.

As documented in aliases(5), when an alias name has a
companion alias named owner-name, this will replace the
envelope sender address, so that delivery errors will be
reported to the owner alias instead of the sender. This configuration
is recommended for mailing lists.

A less known property of the owner alias is that it also forces
the local(8) delivery agent to write local and remote addresses
from alias expansion to a new queue file, instead of attempting to
deliver mail to local addresses as soon as they come out of alias
expansion.

Writing local addresses from alias expansion to a new queue
file allows for robust handling of temporary delivery errors: errors
with one local member have no effect on deliveries to other members
of the list. On the other hand, delivery to local addresses as
soon as they come out of alias expansion is fragile: a temporary
error with one local address from alias expansion will cause the
entire alias to be expanded repeatedly until the error goes away,
or until the message expires in the queue. In that case, a problem
with one list member results in multiple message deliveries to other
list members.

The default behavior of Postfix 2.8 and later is to keep the
owner-alias attribute of the parent alias, when delivering mail to
a child alias that does not have its own owner alias. Then, local
addresses from that child alias will be written to a new queue file,
and a temporary error with one local address will not affect delivery
to other mailing list members.

Unfortunately, older Postfix releases reset the owner-alias
attribute when delivering mail to a child alias that does not have
its own owner alias. To be precise, this resets only the decision
to create a new queue file, not the decision to override the envelope
sender address. The local(8) delivery agent then attempts to
deliver local addresses as soon as they come out of child alias
expansion. If delivery to any address from child alias expansion
fails with a temporary error condition, the entire mailing list may
be expanded repeatedly until the mail expires in the queue, resulting
in multiple deliveries of the same message to mailing list members.


(default: yes)

Resolve a recipient address safely instead of correctly, by
looking inside quotes.

By default, the Postfix address resolver does not quote the
address localpart as per RFC 822, so that additional @ or % or !
operators remain visible. This behavior is safe but it is also
technically incorrect.

If you specify “resolve_dequoted_address = no”, then
the Postfix
resolver will not know about additional @ etc. operators in the
address localpart. This opens opportunities for obscure mail relay
attacks with user@domain@domain addresses when Postfix provides
backup MX service for Sendmail systems.


(default: no)

Resolve an address that ends in the “@” null domain as if the
local hostname were specified, instead of rejecting the address as
invalid.

This feature is available in Postfix 2.1 and later.
Earlier versions always resolve the null domain as the local
hostname.

The Postfix SMTP server uses this feature to reject mail from
or to addresses that end in the “@” null domain, and from addresses
that rewrite into a form that ends in the “@” null domain.


(default: no)

Resolve “user@ipaddress” as “user@[ipaddress]”, instead of
rejecting the address as invalid.

This feature is available in Postfix 2.3 and later.


(default: see ‘postconf -d’ output)

Avoid logging that implies white is better than black. Instead
use ‘allowlist’, ‘denylist’, and variations of those words.

This feature is available in Postfix 3.6 and later.


(default: rewrite)

The name of the address rewriting service. This service rewrites
addresses to standard form and resolves them to a (delivery method,
next-hop host, recipient) triple.

This feature is available in Postfix 2.0 and later.


(default: /etc/postfix)

The name of the directory with example Postfix configuration files.
Starting with Postfix 2.1, these files have been replaced with the
postconf(5) manual page.


(default: no)

When authenticating to a remote SMTP or LMTP server with the
default setting “no”, send no SASL authoriZation ID (authzid); send
only the SASL authentiCation ID (authcid) plus the authcid’s password.

The non-default setting “yes” enables the behavior of older
Postfix versions. These always send a SASL authzid that is equal
to the SASL authcid, but this causes interoperability problems
with some SMTP servers.

This feature is available in Postfix 2.4.4 and later.


(default: no)

This parameter should not be used. It was replaced by sender_dependent_relayhost_maps
in Postfix version 2.3.


(default: empty)

Optional BCC (blind carbon-copy) address lookup tables, indexed
by sender address. The BCC address (multiple results are not
supported) is added when mail enters from outside of Postfix.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

The table search order is as follows:

Note: with Postfix 2.3 and later the BCC address is added as if it
was specified with NOTIFY=NONE. The sender will not be notified
when the BCC address is undeliverable, as long as all down-stream
software implements RFC 3461.

Note: with Postfix 2.2 and earlier the sender will be notified
when the BCC address is undeliverable.

Note: automatic BCC recipients are produced only for new mail.
To avoid mailer loops, automatic BCC recipients are not generated
after Postfix forwards mail internally, or after Postfix generates
mail itself.

Example:

sender_bcc_maps = hash:/etc/postfix/sender_bcc

After a change, run “postmap /etc/postfix/sender_bcc“.

This feature is available in Postfix 2.1 and later.


(default: envelope_sender, header_sender)

What addresses are subject to sender_canonical_maps address
mapping. By default, sender_canonical_maps address mapping is
applied to envelope sender addresses, and to header sender addresses.

Specify one or more of: envelope_sender, header_sender

This feature is available in Postfix 2.2 and later.


(default: empty)

Optional address mapping lookup tables for envelope and header
sender addresses.
The table format and lookups are documented in canonical(5).

Example: you want to rewrite the SENDER address “user@ugly.domain”
to “user@pretty.domain”, while still being able to send mail to
the RECIPIENT address “user@ugly.domain”.

Note: $sender_canonical_maps is processed before $canonical_maps.

Example:

sender_canonical_maps = hash:/etc/postfix/sender_canonical

(default: empty)

A sender-dependent override for the global default_transport
parameter setting. The tables are searched by the envelope sender
address and @domain. A lookup result of DUNNO terminates the search
without overriding the global default_transport parameter setting.
This information is overruled with the transport(5) table.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

Note: this overrides default_transport, not transport_maps, and
therefore the expected syntax is that of default_transport, not the
syntax of transport_maps. Specifically, this does not support the
transport_maps syntax for null transport, null nexthop, or null
email addresses.

For safety reasons, this feature does not allow $number
substitutions in regular expression maps.

This feature is available in Postfix 2.7 and later.


(default: empty)

A sender-dependent override for the global relayhost parameter
setting. The tables are searched by the envelope sender address and
@domain. A lookup result of DUNNO terminates the search without
overriding the global relayhost parameter setting (Postfix 2.6 and
later). This information is overruled with relay_transport,
sender_dependent_default_transport_maps, default_transport and with
the transport(5) table.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

For safety reasons, this feature does not allow $number
substitutions in regular expression maps.

This feature is available in Postfix 2.3 and later.


(default: always)

Controls how the Postfix sendmail command converts email message
line endings from <CR><LF> into UNIX format (<LF>).

always
Always convert message lines ending
in <CR><LF>. This setting is the default with Postfix
2.9 and later.
strict
Convert message lines ending in
<CR><LF> only if the first input line ends in
<CR><LF>. This setting is backwards-compatible with
Postfix 2.8 and earlier.
never
Never convert message lines ending in
<CR><LF>. This setting exists for completeness only.

This feature is available in Postfix 2.9 and later.


(default: see “postconf -d” output)

A Sendmail compatibility feature that specifies the location of
the Postfix sendmail(1) command. This command can be used to
submit mail into the Postfix queue.


(read-only)

The master.cf service name of a Postfix daemon process. This
can be used to distinguish the logging from different services that
use the same program name.

Example master.cf entries:

# Distinguish inbound MTA logging from submission and smtps logging.
smtp      inet  n       -       n       -       -       smtpd
submission inet n       -       n       -       -       smtpd
    -o syslog_name=postfix/$service_name
smtps     inet  n       -       n       -       -       smtpd
    -o syslog_name=postfix/$service_name
# Distinguish outbound MTA logging from inbound relay logging.
smtp      unix  -       -       n       -       -       smtp
relay     unix  -       -       n       -       -       smtp
    -o syslog_name=postfix/$service_name

(default: 60s)

How long the Postfix master(8) waits before forking a server that
appears to be malfunctioning.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: postdrop)

The group ownership of set-gid Postfix commands and of group-writable
Postfix directories. When this parameter value is changed you need
to re-run “postfix set-permissions” (with Postfix version 2.0 and
earlier: “/etc/postfix/post-install set-permissions“.


(default: see ‘postconf -d’ output)

The location of Postfix dynamically-linked libraries
(libpostfix-*.so), and the default location of Postfix database
plugins (postfix-*.so) that have a relative pathname in the
dynamicmaps.cf file. The shlib_directory parameter defaults to
“no” when Postfix dynamically-linked libraries and database plugins
are disabled at compile time, otherwise it typically defaults to
/usr/lib/postfix or /usr/local/lib/postfix.

Notes:

This feature is available in Postfix 3.0 and later.


(default: yes)

Display the name of the recipient table in the “User unknown”
responses. The extra detail makes troubleshooting easier but also
reveals information that is nobody else’s business.

This feature is available in Postfix 2.0 and later.


(default: showq)

The name of the showq(8) service. This service produces mail queue
status reports.

This feature is available in Postfix 2.0 and later.


(default: any)

The address type (“ipv6”, “ipv4” or “any”) that the Postfix
SMTP client will try first, when a destination has IPv6 and IPv4
addresses with equal MX preference. This feature has no effect
unless the inet_protocols setting enables both IPv4 and IPv6.

Postfix SMTP client address preference has evolved. With Postfix
2.8 the default is “ipv6”; earlier implementations are hard-coded
to prefer IPv6 over IPv4.

Notes for mail delivery between sites that have both IPv4 and
IPv6 connectivity:

This feature is available in Postfix 2.8 and later.


(default: rcpt)

In the context of email address verification, the SMTP protocol
stage that determines whether an email address is deliverable.
Specify one of “rcpt” or “data”. The latter is needed with remote
SMTP servers that reject recipients after the DATA command. Use
transport_maps to apply this feature selectively:

/etc/postfix/main.cf:
    transport_maps = hash:/etc/postfix/transport

/etc/postfix/transport:
    smtp-domain-that-verifies-after-data    smtp-data-target:
    lmtp-domain-that-verifies-after-data    lmtp-data-target:

/etc/postfix/master.cf:
    smtp-data-target    unix    -    -    n    -    -    smtp
        -o smtp_address_verify_target=data
    lmtp-data-target    unix    -    -    n    -    -    lmtp
        -o lmtp_address_verify_target=data

Unselective use of the “data” target does no harm, but will
result in unnecessary “lost connection after DATA” events at remote
SMTP/LMTP servers.

This feature is available in Postfix 3.0 and later.


(default: yes)

Always send EHLO at the start of an SMTP session.

With “smtp_always_send_ehlo = no”, the Postfix SMTP client sends
EHLO only when
the word “ESMTP” appears in the server greeting banner (example:
220 spike.porcupine.org ESMTP Postfix).


(default: yes)

When a remote destination resolves to a combination of IPv4 and
IPv6 addresses, ensure that the Postfix SMTP client can try both
address types before it runs into the smtp_mx_address_limit.

This avoids an interoperability problem when a destination resolves
to primarily IPv6 addresses, the smtp_address_limit feature eliminates
most or all IPv4 addresses, and the destination is not reachable over
IPv6.

This feature is available in Postfix 3.3 and later.


(default: empty)

An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv4 connection.

This can be specified in the main.cf file for all SMTP clients, or
it can be specified in the master.cf file for a specific client,
for example:

/etc/postfix/master.cf:
    smtp ... smtp -o smtp_bind_address=11.22.33.44

See smtp_bind_address_enforce for how Postfix should handle
errors (Postfix 3.7 and later).

Note 1: when inet_interfaces specifies no more than one IPv4
address, and that address is a non-loopback address, it is
automatically used as the smtp_bind_address. This supports virtual
IP hosting, but can be a problem on multi-homed firewalls. See the
inet_interfaces documentation for more detail.

Note 2: address information may be enclosed inside [],
but this form is not required here.


(default: empty)

An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv6 connection.

This feature is available in Postfix 2.2 and later.

This can be specified in the main.cf file for all SMTP clients, or
it can be specified in the master.cf file for a specific client,
for example:

/etc/postfix/master.cf:
    smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

See smtp_bind_address_enforce for how Postfix should handle
errors (Postfix 3.7 and later).

Note 1: when inet_interfaces specifies no more than one IPv6
address, and that address is a non-loopback address, it is
automatically used as the smtp_bind_address6. This supports virtual
IP hosting, but can be a problem on multi-homed firewalls. See the
inet_interfaces documentation for more detail.

Note 2: address information may be enclosed inside [],
but this form is not recommended here.


(default: no)

Defer delivery when the Postfix SMTP client cannot apply the
smtp_bind_address or smtp_bind_address6 setting. By default, the
Postfix SMTP client will continue delivery after logging a warning.

This feature is available in Postfix 3.7 and later.


(default: empty)

Restricted body_checks(5) tables for the Postfix SMTP client.
These tables are searched while mail is being delivered. Actions
that change the delivery time or destination are not available.

This feature is available in Postfix 2.5 and later.


(default: version dependent)

When the remote SMTP servername is a DNS CNAME, replace the
servername with the result from CNAME expansion for the purpose of
logging, SASL password lookup, TLS
policy decisions, or TLS certificate verification. The value “no”
hardens Postfix smtp_tls_per_site hostname-based policies against
false hostname information in DNS CNAME records, and makes SASL
password file lookups more predictable. This is the default setting
as of Postfix 2.3.

When DNS CNAME records are validated with secure DNS lookups
(smtp_dns_support_level = dnssec), they are always allowed to
override the above servername (Postfix 2.11 and later).

This feature is available in Postfix 2.2.9 and later.


(default: 30s)

The Postfix SMTP client time limit for completing a TCP connection, or
zero (use the operating system built-in time limit).

When no connection can be made within the deadline, the Postfix
SMTP client
tries the next address on the mail exchanger list. Specify 0 to
disable the time limit (i.e. use whatever timeout is implemented by
the operating system).

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

Permanently enable SMTP connection caching for the specified
destinations. With SMTP connection caching, a connection is not
closed immediately after completion of a mail transaction. Instead,
the connection is kept open for up to $smtp_connection_cache_time_limit
seconds. This allows connections to be reused for other deliveries,
and can improve mail delivery performance.

Specify a comma or white space separated list of destinations
or pseudo-destinations:

This feature is available in Postfix 2.2 and later.


(default: yes)

Temporarily enable SMTP connection caching while a destination
has a high volume of mail in the active queue. With SMTP connection
caching, a connection is not closed immediately after completion
of a mail transaction. Instead, the connection is kept open for
up to $smtp_connection_cache_time_limit seconds. This allows
connections to be reused for other deliveries, and can improve mail
delivery performance.

This feature is available in Postfix 2.2 and later.


(default: 2s)

When SMTP connection caching is enabled, the amount of time that
an unused SMTP client socket is kept open before it is closed. Do
not specify larger values without permission from the remote sites.

This feature is available in Postfix 2.2 and later.


(default: 0)

When SMTP connection caching is enabled, the number of times
that an SMTP session may be reused before it is closed, or zero (no
limit). With a reuse count limit of N, a connection is used up to
N 1 times.

NOTE: This feature is unsafe. When a high-volume destination
has multiple inbound MTAs, then the slowest inbound MTA will attract
the most connections to that destination. This limitation does not
exist with the smtp_connection_reuse_time_limit feature.

This feature is available in Postfix 2.11.


(default: 300s)

The amount of time during which Postfix will use an SMTP
connection repeatedly. The timer starts when the connection is
initiated (i.e. it includes the connect, greeting and helo latency,
in addition to the latencies of subsequent mail delivery transactions).

This feature addresses a performance stability problem with
remote SMTP servers. This problem is not specific to Postfix: it
can happen when any MTA sends large amounts of SMTP email to a site
that has multiple MX hosts.

The problem starts when one of a set of MX hosts becomes slower
than the rest. Even though SMTP clients connect to fast and slow
MX hosts with equal probability, the slow MX host ends up with more
simultaneous inbound connections than the faster MX hosts, because
the slow MX host needs more time to serve each client request.

The slow MX host becomes a connection attractor. If one MX
host becomes N times slower than the rest, it dominates mail delivery
latency unless there are more than N fast MX hosts to counter the
effect. And if the number of MX hosts is smaller than N, the mail
delivery latency becomes effectively that of the slowest MX host
divided by the total number of MX hosts.

The solution uses connection caching in a way that differs from
Postfix version 2.2. By limiting the amount of time during which a connection
can be used repeatedly (instead of limiting the number of deliveries
over that connection), Postfix not only restores fairness in the
distribution of simultaneous connections across a set of MX hosts,
it also favors deliveries over connections that perform well, which
is exactly what we want.

The default reuse time limit, 300s, is comparable to the various
smtp transaction timeouts which are fair estimates of maximum excess
latency for a slow delivery. Note that hosts may accept thousands
of messages over a single connection within the default connection
reuse time limit. This number is much larger than the default Postfix
version 2.2 limit of 10 messages per cached connection. It may prove necessary
to lower the limit to avoid interoperability issues with MTAs that
exhibit bugs when many messages are delivered via a single connection.
A lower reuse time limit risks losing the benefit of connection
reuse when the average connection and mail delivery latency exceeds
the reuse time limit.

This feature is available in Postfix 2.3 and later.


(default: 600s)

The Postfix SMTP client time limit for sending the SMTP “.”, and
for receiving the remote SMTP server response.

When no response is received within the deadline, a warning is
logged that the mail may be delivered multiple times.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 120s)

The Postfix SMTP client time limit for sending the SMTP DATA command,
and for receiving the remote SMTP server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: 180s)

The Postfix SMTP client time limit for sending the SMTP message content.
When the connection makes no progress for more than $smtp_data_xfer_timeout
seconds the Postfix SMTP client terminates the transfer.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: no)

Defer mail delivery when no MX record resolves to an IP address.

The default (no) is to return the mail as undeliverable. With older
Postfix versions the default was to keep trying to deliver the mail
until someone fixed the MX record or until the mail was too old.

Note: the Postfix SMTP client always ignores MX records with equal
or worse preference
than the local MTA itself.

This feature is available in Postfix 2.1 and later.


(default: $default_delivery_status_filter)

Optional filter for the smtp(8) delivery agent to change the
delivery status code or explanatory text of successful or unsuccessful
deliveries. See default_delivery_status_filter for details.

NOTE: This feature modifies Postfix SMTP client error or non-error
messages that may or may not be derived from remote SMTP server
responses. In contrast, the smtp_reply_filter feature modifies
remote SMTP server responses only.


(default: $default_destination_concurrency_limit)

The maximal number of parallel deliveries to the same destination
via the smtp message delivery transport. This limit is enforced by
the queue manager. The message delivery transport name is the first
field in the entry in the master.cf file.


(default: $default_destination_recipient_limit)

The maximal number of recipients per message for the smtp
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.

Setting this parameter to a value of 1 changes the meaning of
smtp_destination_concurrency_limit from concurrency per domain
into concurrency per recipient.


(default: empty)

Lookup tables, indexed by the remote SMTP server address, with
case insensitive lists of EHLO keywords (pipelining, starttls, auth,
etc.) that the Postfix SMTP client will ignore in the EHLO response from a
remote SMTP server. See smtp_discard_ehlo_keywords for details. The
table is not indexed by hostname for consistency with
smtpd_discard_ehlo_keyword_address_maps.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

This feature is available in Postfix 2.2 and later.


(default: empty)

A case insensitive list of EHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix SMTP client will ignore in the EHLO
response from a remote SMTP server.

This feature is available in Postfix 2.2 and later.

Notes:


(default: empty)

Optional filter for Postfix SMTP client DNS lookup results.
Specify zero or more lookup tables. The lookup tables are searched
in the given order for a match with the DNS lookup result, converted
to the following form:

name ttl class type preference value

The class field is always “IN”, the preference
field exists only for MX records, the names of hosts, domains, etc.
end in “.”, and those names are in ASCII form (xn--mumble form in
the case of UTF8 names).

When a match is found, the table lookup result specifies an
action. By default, the table query and the action name are
case-insensitive. Currently, only the IGNORE action is
implemented.

Notes:

  • Postfix DNS reply filters have no effect on implicit DNS
    lookups through nsswitch.conf or equivalent mechanisms.

  • The Postfix SMTP/LMTP client uses smtp_dns_reply_filter
    and lmtp_dns_reply_filter only to discover a remote SMTP or LMTP
    service (record types MX, A, AAAA, and TLSA). These lookups are
    also made to implement the features reject_unverified_sender and
    reject_unverified_recipient.

  • The Postfix SMTP/LMTP client defers mail delivery when
    a filter removes all lookup results from a successful query.

  • Postfix SMTP server uses smtpd_dns_reply_filter only to
    look up MX, A, AAAA, and TXT records to implement the features
    reject_unknown_helo_hostname, reject_unknown_sender_domain,
    reject_unknown_recipient_domain, reject_rbl_*, and reject_rhsbl_*.

  • The Postfix SMTP server logs a warning or defers mail
    delivery when a filter removes all lookup results from a successful
    query.

Example: ignore Google AAAA records in Postfix SMTP client DNS
lookups, because Google sometimes hard-rejects mail from IPv6 clients
with valid PTR etc. records.

/etc/postfix/main.cf:
    smtp_dns_reply_filter = pcre:/etc/postfix/smtp_dns_reply_filter
/etc/postfix/smtp_dns_reply_filter:
    # /domain ttl IN AAAA address/ action, all case-insensitive.
    # Note: the domain name ends in ".".
    /^S .google.com.s S s S s AAAAs / IGNORE

This feature is available in Postfix 3.0 and later.


(default: empty)

DNS Resolver options for the Postfix SMTP client. Specify zero
or more of the following options, separated by comma or whitespace.
Option names are case-sensitive. Some options refer to domain names
that are specified in the file /etc/resolv.conf or equivalent.

res_defnames
Append the current domain name to single-component names (those
that do not contain a “.” character). This can produce incorrect
results, and is the hard-coded behavior prior to Postfix 2.8.
res_dnsrch
Search for host names in the current domain and in parent
domains. This can produce incorrect results and is therefore not
recommended.

This feature is available in Postfix 2.8 and later.


(default: empty)

Level of DNS support in the Postfix SMTP client. With
smtp_dns_support_level” left at its empty default value, the legacy
disable_dns_lookups” parameter controls whether DNS is enabled in
the Postfix SMTP client, otherwise the legacy parameter is ignored.

Specify one of the following:

disabled
Disable DNS lookups. No MX lookups are performed and hostname
to address lookups are unconditionally “native”. This setting is
not appropriate for hosts that deliver mail to the public Internet.
Some obsolete how-to documents recommend disabling DNS lookups in
some configurations with content_filters. This is no longer required
and strongly discouraged.
enabled
Enable DNS lookups. Nexthop destination domains not enclosed
in “[]” will be subject to MX lookups. If “dns” and “native” are
included in the “smtp_host_lookup” parameter value, DNS will be
queried first to resolve MX-host A records, followed by “native”
lookups if no answer is found in DNS.
dnssec
Enable DNSSEC
lookups. The “dnssec” setting differs from the “enabled” setting
above in the following ways:

The Postfix SMTP client considers non-MX “[nexthop]” and
“[nexthop]:port” destinations equivalent to statically-validated
MX records of the form “nexthop. IN MX 0 nexthop.” Therefore,
with “dnssec” support turned on, validated hostname-to-address
lookups apply to the nexthop domain of any “[nexthop]” or
“[nexthop]:port” destination. This is also true for LMTP “inet:host”
and “inet:host:port” destinations, as LMTP hostnames are never
subject to MX lookups.

The “dnssec” setting is recommended only if you plan to use the
dane or dane-only TLS security
level, otherwise enabling DNSSEC support in Postfix offers no
additional security. Postfix DNSSEC support relies on an upstream
recursive nameserver that validates DNSSEC signatures. Such a DNS
server will always filter out forged DNS responses, even when Postfix
itself is not configured to use DNSSEC.

When using Postfix DANE support the “smtp_host_lookup” parameter
should include “dns”, as DANE is not applicable
to hosts resolved via “native” lookups.

As mentioned above, Postfix is not a validating stub
resolver
; it relies on the system’s configured DNSSEC-validating
recursive
nameserver
to perform all DNSSEC validation. Since this
nameserver’s DNSSEC-validated responses will be fully trusted, it
is strongly recommended that the MTA host have a local DNSSEC-validating
recursive caching nameserver listening on a loopback address, and
be configured to use only this nameserver for all lookups. Otherwise,
Postfix may remain subject to man-in-the-middle attacks that forge
responses from the recursive nameserver

DNSSEC support requires a version of Postfix compiled against a
reasonably-modern DNS resolver(3) library that implements the
RES_USE_DNSSEC and RES_USE_EDNS0 resolver options.

This feature is available in Postfix 2.11 and later.


(default: no)

Enforcement mode: require that remote SMTP servers use TLS
encryption, and never send mail in the clear. This also requires
that the remote SMTP server hostname matches the information in
the remote server certificate, and that the remote SMTP server
certificate was issued by a CA that is trusted by the Postfix SMTP
client. If the certificate doesn’t verify or the hostname doesn’t
match, delivery is deferred and mail stays in the queue.

The server hostname is matched against all names provided as
dNSNames in the SubjectAlternativeName. If no dNSNames are specified,
the CommonName is checked. The behavior may be changed with the
smtp_tls_enforce_peername option.

This option is useful only if you are definitely sure that you
will only connect to servers that support RFC 2487 _and_ that
provide valid server certificates. Typical use is for clients that
send all their email to a dedicated mailhub.

This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_security_level instead.


(default: $fallback_relay)

Optional list of relay destinations that will be used when an
SMTP destination is not found, or when delivery fails due to a
non-permanent error. With Postfix 2.2 and earlier this parameter
is called fallback_relay.

By default, smtp_fallback_relay is empty, mail is returned to
the sender when a destination is not found, and delivery is deferred
after it fails due to a non-permanent error.

With bulk email deliveries, it can be beneficial to run the
fallback relay MTA on the same host, so that it can reuse the sender
IP address. This speeds up deliveries that are delayed by IP-based
reputation systems (greylist, etc.).

The fallback relays must be SMTP destinations. Specify a domain,
host, host:port, [host]:port, [address] or [address]:port; the form
[host] turns off MX lookups. If you specify multiple SMTP
destinations, Postfix will try them in the specified order.

To prevent mailer loops between MX hosts and fall-back hosts,
Postfix version 2.2 and later will not use the fallback relays for
destinations that it is MX host for (assuming DNS lookup is turned on).


(default: empty)

Optional lookup tables that perform address rewriting in the
Postfix SMTP client, typically to transform a locally valid address into
a globally valid address when sending mail across the Internet.
This is needed when the local machine does not have its own Internet
domain name, but uses something like localdomain.local
instead.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

The table format and lookups are documented in generic(5);
examples are shown in the ADDRESS_REWRITING_README and
STANDARD_CONFIGURATION_README documents.

This feature is available in Postfix 2.2 and later.


(default: empty)

Restricted header_checks(5) tables for the Postfix SMTP client.
These tables are searched while mail is being delivered. Actions
that change the delivery time or destination are not available.

This feature is available in Postfix 2.5 and later.


(default: $myhostname)

The hostname to send in the SMTP HELO or EHLO command.

The default value is the machine hostname. Specify a hostname or
[ip.add.re.ss].

This information can be specified in the main.cf file for all SMTP
clients, or it can be specified in the master.cf file for a specific
client, for example:

/etc/postfix/master.cf:
    mysmtp ... smtp -o smtp_helo_name=foo.bar.com

This feature is available in Postfix 2.0 and later.


(default: 300s)

The Postfix SMTP client time limit for sending the HELO or EHLO command,
and for receiving the initial remote SMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: dns)

What mechanisms the Postfix SMTP client uses to look up a host’s
IP address. This parameter is ignored when DNS lookups are disabled
(see: disable_dns_lookups and smtp_dns_support_level). The “dns”
mechanism is always tried before “native” if both are listed.

Specify one of the following:

dns
Hosts can be found in the DNS (preferred).
native
Use the native naming service only (nsswitch.conf, or equivalent
mechanism).
dns, native
Use the native service for hosts not found in the DNS.

This feature is available in Postfix 2.1 and later.


(default: 998)

The maximal length of message header and body lines that Postfix
will send via SMTP. This limit does not include the <CR><LF>
at the end of each line. Longer lines are broken by inserting
“<CR><LF><SPACE>”, to minimize the damage to MIME
formatted mail. Specify zero to disable this limit.

The Postfix limit of 998 characters not including <CR><LF>
is consistent with the SMTP limit of 1000 characters including
<CR><LF>. The Postfix limit was 990 with Postfix 2.8
and earlier.


(default: 300s)

The Postfix SMTP client time limit for sending the MAIL FROM command,
and for receiving the remote SMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

Restricted mime_header_checks(5) tables for the Postfix SMTP
client. These tables are searched while mail is being delivered.
Actions that change the delivery time or destination are not
available.

This feature is available in Postfix 2.5 and later.


(default: 500)

The minimum plaintext data transfer rate in bytes/second for
DATA requests, when deadlines are enabled with smtp_per_request_deadline.
After a write operation transfers N plaintext message bytes (possibly
after TLS encryption), and after the DATA request deadline is
decremented by the elapsed time of that write operation, the DATA
request deadline is incremented by N/smtp_min_data_rate seconds.
However, the deadline will never be incremented beyond the time
limit specified with smtp_data_xfer_timeout.

This feature is available in Postfix 3.7 and later.


(default: 5)

The maximal number of MX (mail exchanger) IP addresses that can
result from Postfix SMTP client mail exchanger lookups, or zero (no
limit). Prior to
Postfix version 2.3, this limit was disabled by default.

This feature is available in Postfix 2.1 and later.


(default: 2)

The maximal number of SMTP sessions per delivery request before
the Postfix SMTP client
gives up or delivers to a fall-back relay host, or zero (no
limit). This restriction ignores sessions that fail to complete the
SMTP initial handshake (Postfix version 2.2 and earlier) or that fail to
complete the EHLO and TLS handshake (Postfix version 2.3 and later).

This feature is available in Postfix 2.1 and later.


(default: empty)

Restricted nested_header_checks(5) tables for the Postfix SMTP
client. These tables are searched while mail is being delivered.
Actions that change the delivery time or destination are not
available.

This feature is available in Postfix 2.5 and later.


(default: no)

Never send EHLO at the start of an SMTP session. See also the
smtp_always_send_ehlo parameter.


(default: no)

Change the behavior of the smtp_*_timeout time limits, from a
time limit per read or write system call, to a time limit to send
or receive a complete record (an SMTP command line, SMTP response
line, SMTP message content line, or TLS protocol message). This
limits the impact from hostile peers that trickle data one byte at
a time.

Note: when per-record deadlines are enabled, a short timeout
may cause problems with TLS over very slow network connections.
The reasons are that a TLS protocol message can be up to 16 kbytes
long (with TLSv1), and that an entire TLS protocol message must be
sent or received within the per-record deadline.

This feature is available in Postfix 2.9-3.6. With older
Postfix releases, the behavior is as if this parameter is set to
“no”. Postfix 3.7 and later use smtp_per_request_deadline.


(default: no)

Change the behavior of the smtp_*_timeout time limits, from a
time limit per plaintext or TLS read or write call, to a combined
time limit for sending a complete SMTP request and for receiving a
complete SMTP response. The deadline limits only the time spent
waiting for plaintext or TLS read or write calls, not time spent
elsewhere. The per-request deadline limits the impact from hostile
peers that trickle data one byte at a time.

See smtp_min_data_rate for how the per-request deadline is
managed during the DATA phase.

Note: when per-request deadlines are enabled, a short time limit
may cause problems with TLS over very slow network connections. The
reason is that a TLS protocol message can be up to 16 kbytes long
(with TLSv1), and that an entire TLS protocol message must be
transferred within the per-request deadline.

This feature is available in Postfix 3.7 and later. A weaker
feature, called smtp_per_record_deadline, is available with Postfix
2.9-3.6.

This feature is available in Postfix 3.7 and later.


(default: 10s)

How long the Postfix SMTP client pauses before sending
“.<CR><LF>” in order to work around the PIX firewall
“<CR><LF>.<CR><LF>” bug.

Choosing too short a time makes this workaround ineffective when
sending large messages over slow network connections.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

Lookup tables, indexed by the remote SMTP server address, with
per-destination workarounds for CISCO PIX firewall bugs. The table
is not indexed by hostname for consistency with
smtp_discard_ehlo_keyword_address_maps.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

This feature is available in Postfix 2.4 and later.


(default: 500s)

How long a message must be queued before the Postfix SMTP client
turns on the PIX firewall “<CR><LF>.<CR><LF>”
bug workaround for delivery through firewalls with “smtp fixup”
mode turned on.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

By default, the workaround is turned off for mail that is queued
for less than 500 seconds. In other words, the workaround is normally
turned off for the first delivery attempt.

Specify 0 to enable the PIX firewall
“<CR><LF>.<CR><LF>” bug workaround upon the
first delivery attempt.


(default: disable_esmtp, delay_dotcrlf)

A list that specifies zero or more workarounds for CISCO PIX
firewall bugs. These workarounds are implemented by the Postfix
SMTP client. Workaround names are separated by comma or space, and
are case insensitive. This parameter setting can be overruled with
per-destination smtp_pix_workaround_maps settings.

delay_dotcrlf
Insert a delay before sending
“.<CR><LF>” after the end of the message content. The
delay is subject to the smtp_pix_workaround_delay_time and
smtp_pix_workaround_threshold_time parameter settings.
disable_esmtp
Disable all extended SMTP commands:
send HELO instead of EHLO.

This feature is available in Postfix 2.4 and later. The default
settings are backwards compatible with earlier Postfix versions.


(default: 300s)

The Postfix SMTP client time limit for sending the QUIT command,
and for receiving the remote SMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: yes)

Quote addresses in Postfix SMTP client MAIL FROM and RCPT TO commands
as required
by RFC 5321. This includes putting quotes around an address localpart
that ends in “.”.

The default is to comply with RFC 5321. If you have to send mail to
a broken SMTP server, configure a special SMTP client in master.cf:

/etc/postfix/master.cf:
    broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

and route mail for the destination in question to the “broken-smtp”
message delivery with a transport(5) table.

This feature is available in Postfix 2.1 and later.


(default: yes)

Randomize the order of equal-preference MX host addresses. This
is a performance feature of the Postfix SMTP client.


(default: 300s)

The Postfix SMTP client time limit for sending the SMTP RCPT TO
command, and for receiving the remote SMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

A mechanism to transform replies from remote SMTP servers one
line at a time. This is a last-resort tool to work around server
replies that break interoperability with the Postfix SMTP client.
Other uses involve fault injection to test Postfix’s handling of
invalid responses.

Notes:

  • In the case of a multi-line reply, the Postfix SMTP client
    uses the final reply line’s numerical SMTP reply code and enhanced
    status code.

  • The numerical SMTP reply code (XYZ) takes precedence over
    the enhanced status code (X.Y.Z). When the enhanced status code
    initial digit differs from the SMTP reply code initial digit, or
    when no enhanced status code is present, the Postfix SMTP client
    uses a generic enhanced status code (X.0.0) instead.

Specify the name of a “type:table” lookup table. The search
string is a single SMTP reply line as received from the remote SMTP
server, except that the trailing <CR><LF> are removed.
When the lookup succeeds, the result replaces the single SMTP reply
line.

Examples:

/etc/postfix/main.cf:
    smtp_reply_filter = pcre:/etc/postfix/reply_filter
/etc/postfix/reply_filter:
    # Transform garbage into "250-filler..." so that it looks like
    # one line from a multi-line reply. It does not matter what we
    # substitute here as long it has the right syntax.  The Postfix
    # SMTP client will use the final line's numerical SMTP reply
    # code and enhanced status code.
    !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

This feature is available in Postfix 2.7.


(default: 20s)

The Postfix SMTP client time limit for sending the RSET command,
and for receiving the remote SMTP server response. The SMTP client
sends RSET in
order to finish a recipient address probe, or to verify that a
cached session is still usable.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: empty)

An optional table to prevent repeated SASL authentication
failures with the same remote SMTP server hostname, username and
password. Each table (key, value) pair contains a server name, a
username and password, and the full server response. This information
is stored when a remote SMTP server rejects an authentication attempt
with a 535 reply code. As long as the smtp_sasl_password_maps
information does not change, and as long as the smtp_sasl_auth_cache_name
information does not expire (see smtp_sasl_auth_cache_time) the
Postfix SMTP client avoids SASL authentication attempts with the
same server, username and password, and instead bounces or defers
mail as controlled with the smtp_sasl_auth_soft_bounce configuration
parameter.

Use a per-destination delivery concurrency of 1 (for example,
smtp_destination_concurrency_limit = 1″,
relay_destination_concurrency_limit = 1″, etc.), otherwise multiple
delivery agents may experience a login failure at the same time.

The table must be accessed via the proxywrite service, i.e. the
map name must start with “proxy:”. The table should be stored under
the directory specified with the data_directory parameter.

This feature uses cryptographic hashing to protect plain-text
passwords, and requires that Postfix is compiled with TLS support.

Example:

smtp_sasl_auth_cache_name = proxy:btree:/var/lib/postfix/sasl_auth_cache

This feature is available in Postfix 2.5 and later.


(default: 90d)

The maximal age of an smtp_sasl_auth_cache_name entry before it
is removed.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

This feature is available in Postfix 2.5 and later.


(default: no)

Enable SASL authentication in the Postfix SMTP client. By default,
the Postfix SMTP client uses no authentication.

Example:

smtp_sasl_auth_enable = yes

(default: yes)

When a remote SMTP server rejects a SASL authentication request
with a 535 reply code, defer mail delivery instead of returning
mail as undeliverable. The latter behavior was hard-coded prior to
Postfix version 2.5.

Note: the setting “yes” overrides the global soft_bounce
parameter, but the setting “no” does not.

Example:

# Default as of Postfix 2.5
smtp_sasl_auth_soft_bounce = yes
# The old hard-coded default
smtp_sasl_auth_soft_bounce = no

This feature is available in Postfix 2.5 and later.


(default: empty)

If non-empty, a Postfix SMTP client filter for the remote SMTP
server’s list of offered SASL mechanisms. Different client and
server implementations may support different mechanism lists; by
default, the Postfix SMTP client will use the intersection of the
two. smtp_sasl_mechanism_filter specifies an optional third mechanism
list to intersect with.

Specify mechanism names, “/file/name” patterns or “type:table
lookup tables. The right-hand side result from “type:table” lookups
is ignored. Specify “!pattern” to exclude a mechanism name from the
list. The form “!/file/name” is supported only in Postfix version
2.4 and later.

This feature is available in Postfix 2.2 and later.

Examples:

smtp_sasl_mechanism_filter = plain, login
smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

(default: empty)

Optional Postfix SMTP client lookup tables with one username:password
entry per sender, remote hostname or next-hop domain. Per-sender
lookup is done only when sender-dependent authentication is enabled.
If no username:password entry is found, then the Postfix SMTP client
will not attempt to authenticate to the remote host.

The Postfix SMTP client opens the lookup table before going to
chroot jail, so you can leave the password file in /etc/postfix.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.


(default: empty)

Implementation-specific information that the Postfix SMTP client
passes through to
the SASL plug-in implementation that is selected with
smtp_sasl_type. Typically this specifies the name of a
configuration file or rendezvous point.

This feature is available in Postfix 2.3 and later.


(default: noplaintext, noanonymous)

Postfix SMTP client SASL security options; as of Postfix 2.3
the list of available
features depends on the SASL client implementation that is selected
with smtp_sasl_type.

The following security features are defined for the cyrus
client SASL implementation:

Specify zero or more of the following:

noplaintext
Disallow methods that use plaintext passwords.
noactive
Disallow methods subject to active (non-dictionary) attack.
nodictionary
Disallow methods subject to passive (dictionary) attack.
noanonymous
Disallow methods that allow anonymous authentication.
mutual_auth
Only allow methods that provide mutual authentication (not
available with SASL version 1).
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Example:

smtp_sasl_security_options = noplaintext

(default: $smtp_sasl_security_options)

The SASL authentication security options that the Postfix SMTP
client uses for TLS encrypted SMTP sessions.

This feature is available in Postfix 2.2 and later.


(default: $smtp_sasl_tls_security_options)

The SASL authentication security options that the Postfix SMTP
client uses for TLS encrypted SMTP sessions with a verified server
certificate.

When mail is sent to the public MX host for the recipient’s
domain, server certificates are by default optional, and delivery
proceeds even if certificate verification fails. For delivery via
a submission service that requires SASL authentication, it may be
appropriate to send plaintext passwords only when the connection
to the server is strongly encrypted and the server identity
is verified.

The smtp_sasl_tls_verified_security_options parameter makes it
possible to only enable plaintext mechanisms when a secure connection
to the server is available. Submission servers subject to this
policy must either have verifiable certificates or offer suitable
non-plaintext SASL mechanisms.

This feature is available in Postfix 2.6 and later.


(default: cyrus)

The SASL plug-in type that the Postfix SMTP client should use
for authentication. The available types are listed with the
postconf -A” command.

This feature is available in Postfix 2.3 and later.


(default: no)

Whether or not to append the “AUTH=<>” option to the MAIL
FROM command in SASL-authenticated SMTP sessions. The default is
not to send this, to avoid problems with broken remote SMTP servers.
Before Postfix 2.9 the behavior is as if “smtp_send_dummy_mail_auth
= yes”.

This feature is available in Postfix 2.9 and later.


(default: no)

Send the non-standard XFORWARD command when the Postfix SMTP server
EHLO response announces XFORWARD support.

This allows a Postfix SMTP delivery agent, used for injecting mail
into
a content filter, to forward the name, address, protocol and HELO
name of the original client to the content filter and downstream
queuing SMTP server. This can produce more useful logging than
localhost[127.0.0.1] etc.

This feature is available in Postfix 2.1 and later.


(default: no)

Enable sender-dependent authentication in the Postfix SMTP client; this is
available only with SASL authentication, and disables SMTP connection
caching to ensure that mail from different senders will use the
appropriate credentials.

This feature is available in Postfix 2.3 and later.


(default: yes)

Skip SMTP servers that greet with a 4XX status code (go away, try
again later).

By default, the Postfix SMTP client moves on the next mail exchanger.
Specify
smtp_skip_4xx_greeting = no” if Postfix should defer delivery
immediately.

This feature is available in Postfix 2.0 and earlier.
Later Postfix versions always skip remote SMTP servers that greet
with a
4XX status code.


(default: yes)

Skip remote SMTP servers that greet with a 5XX status code.

By default, the Postfix SMTP client moves on the next mail
exchanger. Specify “smtp_skip_5xx_greeting = no” if Postfix should
bounce the mail immediately. Caution: the latter behavior appears
to contradict RFC 2821.


(default: yes)

Do not wait for the response to the SMTP QUIT command.


(default: 300s)

Time limit for Postfix SMTP client write and read operations
during TLS startup and shutdown handshake procedures.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.2 and later.


(default: smtp)

The default TCP port that the Postfix SMTP client connects to.
Specify a symbolic name (see services(5)) or a numeric port.


(default: empty)

A file containing CA certificates of root CAs trusted to sign
either remote SMTP server certificates or intermediate CA certificates.
These are loaded into memory before the smtp(8) client enters the
chroot jail. If the number of trusted roots is large, consider using
smtp_tls_CApath instead, but note that the latter directory must be
present in the chroot jail if the smtp(8) client is chrooted. This
file may also be used to augment the client certificate trust chain,
but it is best to include all the required certificates directly in
$smtp_tls_cert_file (or, Postfix ≥ 3.4 $smtp_tls_chain_files).

Specify “smtp_tls_CAfile = /path/to/system_CA_file” to use
ONLY the system-supplied default Certification Authority certificates.

Specify “tls_append_default_CA = no” to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates.

Example:

smtp_tls_CAfile = /etc/postfix/CAcert.pem

This feature is available in Postfix 2.2 and later.


(default: empty)

Directory with PEM format Certification Authority certificates
that the Postfix SMTP client uses to verify a remote SMTP server
certificate. Don’t forget to create the necessary “hash” links
with, for example, “$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs”.

To use this option in chroot mode, this directory (or a copy)
must be inside the chroot jail.

Specify “smtp_tls_CApath = /path/to/system_CA_directory” to
use ONLY the system-supplied default Certification Authority certificates.

Specify “tls_append_default_CA = no” to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates.

Example:

smtp_tls_CApath = /etc/postfix/certs

This feature is available in Postfix 2.2 and later.


(default: no)

Try to detect a mail hijacking attack based on a TLS protocol
vulnerability (CVE-2009-3555), where an attacker prepends malicious
HELO, MAIL, RCPT, DATA commands to a Postfix SMTP client TLS session.
The attack would succeed with non-Postfix SMTP servers that reply
to the malicious HELO, MAIL, RCPT, DATA commands after negotiating
the Postfix SMTP client TLS session.

This feature is available in Postfix 2.7.


(default: empty)

File with the Postfix SMTP client RSA certificate in PEM format.
This file may also contain the Postfix SMTP client private RSA key, and
these may be the same as the Postfix SMTP server RSA certificate and key
file. With Postfix ≥ 3.4 the preferred way to configure client keys
and certificates is via the “smtp_tls_chain_files” parameter.

Do not configure client certificates unless you must present
client TLS certificates to one or more servers. Client certificates are
not usually needed, and can cause problems in configurations that work
well without them. The recommended setting is to let the defaults stand:

smtp_tls_cert_file =
smtp_tls_key_file =
smtp_tls_eccert_file =
smtp_tls_eckey_file =
# Obsolete DSA parameters
smtp_tls_dcert_file =
smtp_tls_dkey_file =
# Postfix ≥ 3.4 interface
smtp_tls_chain_files =

The best way to use the default settings is to comment out the above
parameters in main.cf if present.

To enable remote SMTP servers to verify the Postfix SMTP client
certificate, the issuing CA certificates must be made available to the
server. You should include the required certificates in the client
certificate file, the client certificate first, then the issuing
CA(s) (bottom-up order).

Example: the certificate for “client.example.com” was issued by
“intermediate CA” which itself has a certificate issued by “root CA”.
As the “root” super-user create the client.pem file with:

# umask 077
# cat client_key.pem client_cert.pem intermediate_CA.pem > chain.pem 

If you also want to verify remote SMTP server certificates issued by
these CAs, you can add the CA certificates to the smtp_tls_CAfile, in
which case it is not necessary to have them in the smtp_tls_cert_file,
smtp_tls_dcert_file (obsolete) or smtp_tls_eccert_file.

A certificate supplied here must be usable as an SSL client certificate
and hence pass the “openssl verify -purpose sslclient …” test.

Example:

smtp_tls_cert_file = /etc/postfix/chain.pem

This feature is available in Postfix 2.2 and later.


(default: empty)

List of one or more PEM files, each holding one or more private keys
directly followed by a corresponding certificate chain. The file names
are separated by commas and/or whitespace. This parameter obsoletes the
legacy algorithm-specific key and certificate file settings. When this
parameter is non-empty, the legacy parameters are ignored, and a warning
is logged if any are also non-empty.

With the proliferation of multiple private key algorithms—which,
as of OpenSSL 1.1.1, include DSA (obsolete), RSA, ECDSA, Ed25519
and Ed448—it is increasingly impractical to use separate
parameters to configure the key and certificate chain for each
algorithm. Therefore, Postfix now supports storing multiple keys and
corresponding certificate chains in a single file or in a set of files.

Each key must appear immediately before the corresponding
certificate, optionally followed by additional issuer certificates that
complete the certificate chain for that key. When multiple files are
specified, they are equivalent to a single file that is concatenated
from those files in the given order. Thus, while a key must always
precede its certificate and issuer chain, it can be in a separate file,
so long as that file is listed immediately before the file that holds
the corresponding certificate chain. Once all the files are
concatenated, the sequence of PEM objects must be: key1, cert1,
[chain1], key2, cert2, [chain2], …, keyN, certN, [chainN].

Storing the private key in the same file as the corresponding
certificate is more reliable. With the key and certificate in separate
files, there is a chance that during key rollover a Postfix process
might load a private key and certificate from separate files that don’t
match. Various operational errors may even result in a persistent
broken configuration in which the certificate does not match the private
key.

The file or files must contain at most one key of each type. If,
for example, two or more RSA keys and corresponding chains are listed,
depending on the version of OpenSSL either only the last one will be
used or a configuration error may be detected. Note that while
“Ed25519” and “Ed448” are considered separate algorithms, the various
ECDSA curves (typically one of prime256v1, secp384r1 or secp521r1) are
considered as different parameters of a single “ECDSA” algorithm, so it
is not presently possible to configure keys for more than one ECDSA
curve.

Example (separate files for each key and corresponding certificate chain):

/etc/postfix/main.cf:
    smtp_tls_chain_files =
        ${config_directory}/ed25519.pem,
        ${config_directory}/ed448.pem,
        ${config_directory}/rsa.pem

/etc/postfix/ed25519.pem:
    -----BEGIN PRIVATE KEY-----
    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH Efbz3
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBKzCB3qADAgECAhQaw rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
    ...
    nC0egv51YPDWxEHom4QA
    -----END CERTIFICATE-----

/etc/postfix/ed448.pem:
    -----BEGIN PRIVATE KEY-----
    MEcCAQAwBQYDK2VxBDsEOQf m0P G0qi NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
    ...
    pQcWsx 4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ eeYOxyThMA
    -----END CERTIFICATE-----

/etc/postfix/rsa.pem:
    -----BEGIN PRIVATE KEY-----
    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
    ...
    ahQkZ3 krcaJvDSMgvu0tDc=
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIC DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
    ...
    Rirz15HGVNTK8wzFd nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
    -----END CERTIFICATE-----

Example (all keys and certificates in a single file):

/etc/postfix/main.cf:
    smtp_tls_chain_files = ${config_directory}/chains.pem

/etc/postfix/chains.pem:
    -----BEGIN PRIVATE KEY-----
    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH Efbz3
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBKzCB3qADAgECAhQaw rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
    ...
    nC0egv51YPDWxEHom4QA
    -----END CERTIFICATE-----
    -----BEGIN PRIVATE KEY-----
    MEcCAQAwBQYDK2VxBDsEOQf m0P G0qi NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
    ...
    pQcWsx 4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ eeYOxyThMA
    -----END CERTIFICATE-----
    -----BEGIN PRIVATE KEY-----
    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
    ...
    ahQkZ3 krcaJvDSMgvu0tDc=
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIC DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
    ...
    Rirz15HGVNTK8wzFd nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
    -----END CERTIFICATE-----

This feature is available in Postfix 3.4 and later.


(default: empty)

Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS
cipher list. As this feature applies to all TLS security levels, it is easy
to create interoperability problems by choosing a non-default cipher
list. Do not use a non-default TLS cipher list on hosts that deliver email
to the public Internet: you will be unable to send email to servers that
only support the ciphers you exclude. Using a restricted cipher list
may be more appropriate for an internal MTA, where one can exert some
control over the TLS software and settings of the peer servers.

Note: do not use “” quotes around the parameter value.

This feature is available in Postfix version 2.2. It is not used with
Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead.


(default: medium)

The minimum TLS cipher grade that the Postfix SMTP client
will use with opportunistic TLS encryption. Cipher types listed in
smtp_tls_exclude_ciphers are excluded from the base definition of
the selected cipher grade. The default value is “medium” for
Postfix releases after the middle of 2022, “export” for older
releases.

When TLS is mandatory the cipher grade is chosen via the
smtp_tls_mandatory_ciphers configuration parameter, see there for syntax
details. See smtp_tls_policy_maps for information on how to configure
ciphers on a per-destination basis.

This feature is available in Postfix 2.6 and later. With earlier Postfix
releases only the smtp_tls_mandatory_ciphers parameter is implemented,
and opportunistic TLS always uses “export” or better (i.e. all) ciphers.


(default: no)

Try to make multiple deliveries per TLS-encrypted connection.
This uses the tlsproxy(8) service to encrypt an SMTP connection,
uses the scache(8) service to save that connection, and relies on
hints from the qmgr(8) daemon.

See “Client-side
TLS connection reuse
” for background details.

This feature is available in Postfix 3.4 and later.


(default: see “postconf -d” output)

The TLS policy for MX hosts with “secure” TLSA records when the
nexthop destination security level is dane, but the MX
record was found via an “insecure” MX lookup. The choices are:

may
The TLSA records will be ignored and TLS will be optional. If
the MX host does not appear to support STARTTLS, or the STARTTLS
handshake fails, mail may be sent in the clear.
encrypt
The TLSA records will signal a requirement to use TLS. While
TLS encryption will be required, authentication will not be performed.
dane
The TLSA records will be used just as with “secure” MX records.
TLS encryption will be required, and, if at least one of the TLSA
records is “usable”, authentication will be required. When
authentication succeeds, it will be logged only as “Trusted”, not
“Verified”, because the MX host name could have been forged.

The default setting for Postfix ≥ 3.6 is “dane” with
smtp_tls_security_level = dane”, otherwise “may”. This behavior
was backported to Postfix versions 3.5.9, 3.4.19, 3.3.16. 3.2.21.
With earlier Postfix versions the default setting was always “dane”.

Though with “insecure” MX records an active attacker can
compromise SMTP transport security by returning forged MX records,
such attacks are “tamper-evident” since any forged MX hostnames
will be recorded in the mail logs. Attackers who place a high value
on staying hidden may be deterred from forging MX records.

This feature is available in Postfix 3.1 and later. The may
policy is backwards-compatible with earlier Postfix versions.


(default: empty)

File with the Postfix SMTP client DSA certificate in PEM format.
This file may also contain the Postfix SMTP client private DSA key.
The DSA algorithm is obsolete and should not be used.

See the discussion under smtp_tls_cert_file for more details.

Example:

smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

This feature is available in Postfix 2.2 and later.


(default: $smtp_tls_dcert_file)

File with the Postfix SMTP client DSA private key in PEM format.
This file may be combined with the Postfix SMTP client DSA certificate
file specified with $smtp_tls_dcert_file. The DSA algorithm is obsolete
and should not be used.

The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account (“root”), and no access
to anyone else.

This feature is available in Postfix 2.2 and later.


(default: empty)

File with the Postfix SMTP client ECDSA certificate in PEM format.
This file may also contain the Postfix SMTP client ECDSA private key.
With Postfix ≥ 3.4 the preferred way to configure client keys and
certificates is via the “smtp_tls_chain_files” parameter.

See the discussion under smtp_tls_cert_file for more details.

Example:

smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.


(default: $smtp_tls_eccert_file)

File with the Postfix SMTP client ECDSA private key in PEM format.
This file may be combined with the Postfix SMTP client ECDSA certificate
file specified with $smtp_tls_eccert_file. With Postfix ≥ 3.4 the
preferred way to configure client keys and certificates is via the
smtp_tls_chain_files” parameter.

The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account (“root”), and no access
to anyone else.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.


(default: yes)

With mandatory TLS encryption, require that the remote SMTP
server hostname matches the information in the remote SMTP server
certificate. As of RFC 2487 the requirements for hostname checking
for MTA clients are not specified.

This option can be set to “no” to disable strict peer name
checking. This setting has no effect on sessions that are controlled
via the smtp_tls_per_site table.

Disabling the hostname verification can make sense in a closed
environment where special CAs are created. If not used carefully,
this option opens the danger of a “man-in-the-middle” attack (the
CommonName of this attacker will be logged).

This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_security_level instead.


(default: empty)

List of ciphers or cipher types to exclude from the Postfix
SMTP client cipher
list at all TLS security levels. This is not an OpenSSL cipherlist, it is
a simple list separated by whitespace and/or commas. The elements are a
single cipher, or one or more ” ” separated cipher properties, in which
case only ciphers matching all the properties are excluded.

Examples (some of these will cause problems):

smtp_tls_exclude_ciphers = aNULL
smtp_tls_exclude_ciphers = MD5, DES
smtp_tls_exclude_ciphers = DES MD5
smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtp_tls_exclude_ciphers = kEDH aRSA

The first setting disables anonymous ciphers. The next setting
disables ciphers that use the MD5 digest algorithm or the (single) DES
encryption algorithm. The next setting disables ciphers that use MD5 and
DES together. The next setting disables the two ciphers “AES256-SHA”
and “DES-CBC3-MD5”. The last setting disables ciphers that use “EDH”
key exchange with RSA authentication.

This feature is available in Postfix 2.3 and later.


(default: empty)

List of acceptable remote SMTP server certificate fingerprints for
the “fingerprint” TLS security level (smtp_tls_security_level =
fingerprint). At this security level, Certification Authorities are not
used, and certificate expiration times are ignored. Instead, server
certificates are verified directly via their certificate fingerprint
or public key fingerprint (Postfix 2.9 and later). The fingerprint
is a message digest of the server certificate (or public key). The
digest algorithm is selected via the smtp_tls_fingerprint_digest
parameter.

The colons between each pair of nibbles in the fingerprint value
are optional (Postfix ≥ 3.6). These were required in earlier
Postfix releases.

When an smtp_tls_policy_maps table entry specifies the
“fingerprint” security level, any “match” attributes in that entry specify
the list of valid fingerprints for the corresponding destination. Multiple
fingerprints can be combined with a “|” delimiter in a single match
attribute, or multiple match attributes can be employed.

Example: Certificate fingerprint verification with internal mailhub.
Two matching fingerprints are listed. The relayhost may be multiple
physical hosts behind a load-balancer, each with its own private/public
key and self-signed certificate. Alternatively, a single relayhost may
be in the process of switching from one set of private/public keys to
another, and both keys are trusted just prior to the transition.

relayhost = [mailhub.example.com]
smtp_tls_security_level = fingerprint
smtp_tls_fingerprint_digest = sha256
smtp_tls_fingerprint_cert_match =
    cd:fc:d8:db:f8:c4:82:96:6c:...:28:71:e8:f5:8d:a5:0d:9b:d4:a6
    dd:5c:ef:f5:c3:bc:64:25:36:...:99:36:06:ce:40:ef:de:2e:ad:a4

Example: Certificate fingerprint verification with selected destinations.
As in the example above, we show two matching fingerprints:

/etc/postfix/main.cf:
    smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
    smtp_tls_fingerprint_digest = sha256

/etc/postfix/tls_policy:
    example.com fingerprint
        match=51:e9:af:2e:1e:40:1f:...:64:0a:30:35:2d:09:16:31:5a:eb:82:76
        match=b6:b4:72:34:e2:59:cd:...:c2:ca:63:0d:4d:cc:2c:7d:84:de:e6:2f

This feature is available in Postfix 2.5 and later.


(default: see “postconf -d” output)

The message digest algorithm used to construct remote SMTP server
certificate fingerprints. At the “fingerprint” TLS security level
(smtp_tls_security_level = fingerprint), the server certificate is
verified by directly matching its certificate fingerprint or its public
key fingerprint (Postfix 2.9 and later). The fingerprint is the
message digest of the server certificate (or its public key)
using the selected
algorithm. With a digest algorithm resistant to “second pre-image”
attacks, it is not feasible to create a new public key and a matching
certificate (or public/private key-pair) that has the same fingerprint.

The default algorithm is sha256 with Postfix ≥ 3.6
and the compatibility_level set to 3.6 or higher. With Postfix
≤ 3.5, the default algorithm is md5.

The best-practice algorithm is now sha256. Recent advances in hash
function cryptanalysis have led to md5 and sha1 being deprecated in favor of
sha256. However, as long as there are no known “second pre-image” attacks
against the older algorithms, their use in this context, though not
recommended, is still likely safe.

While additional digest algorithms are often available with OpenSSL’s
libcrypto, only those used by libssl in SSL cipher suites are available to
Postfix. You’ll likely find support for md5, sha1, sha256 and sha512.

To find the fingerprint of a specific certificate file, with a
specific digest algorithm, run:

$ openssl x509 -noout -fingerprint -digest -in certfile.pem

The text to the right of the “=” sign is the desired fingerprint.
For example:

$ openssl x509 -noout -fingerprint -sha256 -in cert.pem
SHA256 Fingerprint=D4:6A:AB:19:24:...:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

To extract the public key fingerprint from an X.509 certificate,
you need to extract the public key from the certificate and compute
the appropriate digest of its DER (ASN.1) encoding. With OpenSSL
the “-pubkey” option of the “x509” command extracts the public
key always in “PEM” format. We pipe the result to another OpenSSL
command that converts the key to DER and then to the “dgst” command
to compute the fingerprint.

The actual command to transform the key to DER format depends on the
version of OpenSSL used. As of OpenSSL 1.0.0, the “pkey” command supports
all key types.

# OpenSSL ≥ 1.0 with SHA-256 fingerprints.
$ openssl x509 -in cert.pem -noout -pubkey |
    openssl pkey -pubin -outform DER |
    openssl dgst -sha256 -c
(stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:...:fc:09:1a:61:98:b5:bc:7c:60:58

The Postfix SMTP server and client log the peer (leaf) certificate
fingerprint and the public key fingerprint when the TLS loglevel is 2 or
higher.

This feature is available in Postfix 2.5 and later.


(default: no)

Lookup the associated DANE TLSA RRset even when a hostname is
not an alias and its address records lie in an unsigned zone. This
is unlikely to ever yield DNSSEC validated results, since child
zones of unsigned zones are also unsigned in the absence of DLV or
locally configured non-root trust-anchors. We anticipate that such
mechanisms will not be used for just the “_tcp” subdomain of a host.
Suppressing the TLSA RRset lookup reduces latency and avoids potential
interoperability problems with nameservers for unsigned zones that
are not prepared to handle the new TLSA RRset.

This feature is available in Postfix 2.11.


(default: $smtp_tls_cert_file)

File with the Postfix SMTP client RSA private key in PEM format.
This file may be combined with the Postfix SMTP client RSA certificate
file specified with $smtp_tls_cert_file. With Postfix ≥ 3.4 the
preferred way to configure client keys and certificates is via the
smtp_tls_chain_files” parameter.

The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account (“root”), and no access
to anyone else.

Example:

smtp_tls_key_file = $smtp_tls_cert_file

This feature is available in Postfix 2.2 and later.


(default: 0)

Enable additional Postfix SMTP client logging of TLS activity.
Each logging level also includes the information that is logged at
a lower logging level.

0 Disable logging of TLS activity.
1 Log only a summary message on TLS handshake completion
— no logging of remote SMTP server certificate trust-chain
verification errors if server certificate verification is not required.
With Postfix 2.8 and earlier, log the summary message and unconditionally
log trust-chain verification errors.
2 Also log levels during TLS negotiation.
3 Also log the hexadecimal and ASCII dump of the
TLS negotiation process.
4 Also log the hexadecimal and ASCII dump of complete
transmission after STARTTLS.

Do not use “smtp_tls_loglevel = 2″ or higher except in case of
problems. Use of loglevel 4 is strongly discouraged.

This feature is available in Postfix 2.2 and later.


(default: medium)

The minimum TLS cipher grade that the Postfix SMTP client will
use with
mandatory TLS encryption. The default value “medium” is suitable
for most destinations with which you may want to enforce TLS, and
is beyond the reach of today’s cryptanalytic methods. See
smtp_tls_policy_maps for information on how to configure ciphers
on a per-destination basis.

The following cipher grades are supported:

export
Enable “EXPORT” grade or better OpenSSL ciphers. The underlying
cipherlist is specified via the tls_export_cipherlist configuration
parameter, which you are strongly encouraged not to change. This
choice is insecure and SHOULD NOT be used.
low
Enable “LOW” grade or better OpenSSL ciphers. The underlying
cipherlist is specified via the tls_low_cipherlist configuration
parameter, which you are strongly encouraged not to change. This
choice is insecure and SHOULD NOT be used.
medium
Enable “MEDIUM” grade or better OpenSSL ciphers.
The underlying cipherlist is specified via the tls_medium_cipherlist
configuration parameter, which you are strongly encouraged not to change.
high
Enable only “HIGH” grade OpenSSL ciphers. This setting may
be appropriate when all mandatory TLS destinations (e.g. when all
mail is routed to a suitably capable relayhost) support at least one
“HIGH” grade cipher. The underlying cipherlist is specified via the
tls_high_cipherlist configuration parameter, which you are strongly
encouraged not to change.
null
Enable only the “NULL” OpenSSL ciphers, these provide authentication
without encryption. This setting is only appropriate in the rare case
that all servers are prepared to use NULL ciphers (not normally enabled
in TLS servers). A plausible use-case is an LMTP server listening on a
UNIX-domain socket that is configured to support “NULL” ciphers. The
underlying cipherlist is specified via the tls_null_cipherlist
configuration parameter, which you are strongly encouraged not to
change.

The underlying cipherlists for grades other than “null” include
anonymous ciphers, but these are automatically filtered out if the
Postfix SMTP client is configured to verify server certificates.
You are very unlikely to need to take any steps to exclude anonymous
ciphers, they are excluded automatically as necessary. If you must
exclude anonymous ciphers at the “may” or “encrypt” security levels,
when the Postfix SMTP client does not need or use peer certificates, set
smtp_tls_exclude_ciphers = aNULL”. To exclude anonymous ciphers only when
TLS is enforced, set “smtp_tls_mandatory_exclude_ciphers = aNULL”.

This feature is available in Postfix 2.3 and later.


(default: empty)

Additional list of ciphers or cipher types to exclude from the
Postfix SMTP client cipher list at mandatory TLS security levels. This list
works in addition to the exclusions listed with smtp_tls_exclude_ciphers
(see there for syntax details).

Starting with Postfix 2.6, the mandatory cipher exclusions can be
specified on a per-destination basis via the TLS policy “exclude”
attribute. See smtp_tls_policy_maps for notes and examples.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

TLS protocols that the Postfix SMTP client will use with mandatory
TLS encryption. In main.cf the values are separated by whitespace,
commas or colons. In the policy table “protocols” attribute (see
smtp_tls_policy_maps) the only valid separator is colon. An empty value
means allow all protocols.

The valid protocol names (see SSL_get_version(3)) are “SSLv2”,
“SSLv3”, “TLSv1”, “TLSv1.1”, “TLSv1.2” and “TLSv1.3”. Starting with
Postfix 3.6, the default value is “>=TLSv1”, which sets TLS 1.0 as
the lowest supported TLS protocol version (see below). Older releases
use the “!” exclusion syntax, also described below.

As of Postfix 3.6, the preferred way to limit the range of
acceptable protocols is to set a lowest acceptable TLS protocol version
and/or a highest acceptable TLS protocol version. To set the lower
bound include an element of the form: “>=version” where
version is a either one of the TLS protocol names listed above,
or a hexadecimal number corresponding to the desired TLS protocol
version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.). For the upper
bound, use “<=version“. There must be no whitespace between
the “>=” or “<=” symbols and the protocol name or number.

Hexadecimal protocol numbers make it possible to specify protocol
bounds for TLS versions that are known to OpenSSL, but might not be
known to Postfix. They cannot be used with the legacy exclusion syntax.
Leading “0” or “0x” prefixes are supported, but not required.
Therefore, “301”, “0301”, “0x301” and “0x0301” are all equivalent to
“TLSv1”. Hexadecimal versions unknown to OpenSSL will fail to set the
upper or lower bound, and a warning will be logged. Hexadecimal
versions should only be used when Postfix is linked with some future
version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
yet support a symbolic name for that protocol version.

Hexadecimal example (Postfix ≥ 3.6):

# Allow only TLS 1.2 through (hypothetical) TLS 1.4, once supported
# in some future version of OpenSSL (presently a warning is logged).
smtp_tls_mandatory_protocols = >=TLSv1.2, <=0305
# Allow only TLS 1.2 and up:
smtp_tls_mandatory_protocols = >=0x0303

With Postfix < 3.6 there is no support for a minimum or maximum
version, and the protocol range is configured via protocol exclusions.
To require at least TLS 1.0, set “smtp_tls_mandatory_protocols = !SSLv2,
!SSLv3″. Listing the protocols to include, rather than the protocols to
exclude, is supported, but not recommended. The exclusion syntax more
accurately matches the underlying OpenSSL interface.

When using the exclusion syntax, take care to ensure that the range
of protocols supported by the Postfix SMTP client is contiguous. When
a protocol version is enabled, disabling any higher version implicitly
disables all versions above that higher version. Thus, for example:

smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1.1

also disables any protocol versions higher than TLSv1.1 leaving
only “TLSv1” enabled.

Support for “TLSv1.3” was introduced in OpenSSL 1.1.1. Disabling
this protocol via “!TLSv1.3” is supported since Postfix 3.4 (or patch
releases ≥ 3.0.14, 3.1.10, 3.2.7 and 3.3.2).

While the vast majority of SMTP servers with DANE TLSA records now
support at least TLS 1.2, a few still only support TLS 1.0. If you use
“dane” or “dane-only” it is best not to disable TLSv1, except perhaps
via the policy table for destinations which you are sure will support
“TLSv1.2”.

See the documentation of the smtp_tls_policy_maps parameter and
TLS_README for more information about security levels.

Example:

# Preferred syntax with Postfix ≥ 3.6:
smtp_tls_mandatory_protocols = >=TLSv1.2, <=TLSv1.3
# Legacy syntax:
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1

This feature is available in Postfix 2.3 and later.


(default: no)

Log the hostname of a remote SMTP server that offers STARTTLS,
when TLS is not already enabled for that server.

The logfile record looks like:

postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]

This feature is available in Postfix 2.2 and later.


(default: empty)

Optional lookup tables with the Postfix SMTP client TLS usage
policy by next-hop destination and by remote SMTP server hostname.
When both lookups succeed, the more specific per-site policy (NONE,
MUST, etc.) overrides the less specific one (MAY), and the more secure
per-site policy (MUST, etc.) overrides the less secure one (NONE).
With Postfix 2.3 and later smtp_tls_per_site is strongly discouraged:
use smtp_tls_policy_maps instead.

Use of the bare hostname as the per-site table lookup key is
discouraged. Always use the full destination nexthop (enclosed in
[] with a possible “:port” suffix). A recipient domain or MX-enabled
transport next-hop with no port suffix may look like a bare hostname,
but is still a suitable destination.

Specify a next-hop destination or server hostname on the left-hand
side; no wildcards are allowed. The next-hop destination is either
the recipient domain, or the destination specified with a transport(5)
table, the relayhost parameter, or the relay_transport parameter.
On the right hand side specify one of the following keywords:

NONE
Don’t use TLS at all. This overrides a less
specific MAY lookup result from the alternate host or next-hop
lookup key, and overrides the global smtp_use_tls, smtp_enforce_tls,
and smtp_tls_enforce_peername settings.
MAY
Try to use TLS if the server announces support,
otherwise use an unencrypted connection. This has less precedence
than a more specific result (including NONE) from the alternate
host or next-hop lookup key, and has less precedence than the more
specific global “smtp_enforce_tls = yes” or “smtp_tls_enforce_peername
= yes”.
MUST_NOPEERMATCH
Require TLS encryption, but do not
require that the remote SMTP server hostname matches the information
in the remote SMTP server certificate, or that the server certificate
was issued by a trusted CA. This overrides a less secure NONE
or a less specific MAY lookup result from the alternate host
or next-hop lookup key, and overrides the global smtp_use_tls,
smtp_enforce_tls and smtp_tls_enforce_peername settings.
MUST
Require TLS encryption, require that the remote
SMTP server hostname matches the information in the remote SMTP
server certificate, and require that the remote SMTP server certificate
was issued by a trusted CA. This overrides a less secure NONE
or MUST_NOPEERMATCH or a less specific MAY lookup
result from the alternate host or next-hop lookup key, and overrides
the global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peername
settings.

The above keywords correspond to the “none”, “may”, “encrypt” and
“verify” security levels for the new smtp_tls_security_level parameter
introduced in Postfix 2.3. Starting with Postfix 2.3, and independently
of how the policy is specified, the smtp_tls_mandatory_ciphers and
smtp_tls_mandatory_protocols parameters apply when TLS encryption
is mandatory. Connections for which encryption is optional typically
enable all “export” grade and better ciphers (see smtp_tls_ciphers
and smtp_tls_protocols).

As long as no secure DNS lookup mechanism is available, false
hostnames in MX or CNAME responses can change the server hostname
that Postfix uses for TLS policy lookup and server certificate
verification. Even with a perfect match between the server hostname and
the server certificate, there is no guarantee that Postfix is connected
to the right server. See TLS_README (Closing a DNS loophole with obsolete
per-site TLS policies) for a possible work-around.

This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_policy_maps instead.


(default: empty)

Optional lookup tables with the Postfix SMTP client TLS security
policy by next-hop destination; when a non-empty value is specified,
this overrides the obsolete smtp_tls_per_site parameter. See
TLS_README for a more detailed discussion of TLS security levels.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

The TLS policy table is indexed by the full next-hop destination,
which is either the recipient domain, or the verbatim next-hop
specified in the transport table, $local_transport, $virtual_transport,
$relay_transport or $default_transport. This includes any enclosing
square brackets and any non-default destination server port suffix. The
LMTP socket type prefix (inet: or unix:) is not included in the lookup
key.

Only the next-hop domain, or $myhostname with LMTP over UNIX-domain
sockets, is used as the nexthop name for certificate verification. The
port and any enclosing square brackets are used in the table lookup key,
but are not used for server name verification.

When the lookup key is a domain name without enclosing square brackets
or any :port suffix (typically the recipient domain), and the full
domain is not found in the table, just as with the transport(5) table,
the parent domain starting with a leading “.” is matched recursively. This
allows one to specify a security policy for a recipient domain and all
its sub-domains.

The lookup result is a security level, followed by an optional list
of whitespace and/or comma separated name=value attributes that override
related main.cf settings. The TLS security levels in order of increasing
security are:

none
No TLS. No additional attributes are supported at this level.
may
Opportunistic TLS. Since sending in the clear is acceptable,
demanding stronger than default TLS security merely reduces
interoperability. The optional “ciphers”, “exclude”, and “protocols”
attributes (available for opportunistic TLS with Postfix ≥ 2.6)
and “connection_reuse” attribute (Postfix ≥ 3.4) override the
smtp_tls_ciphers“, “smtp_tls_exclude_ciphers“, “smtp_tls_protocols“,
and
smtp_tls_connection_reuse” configuration parameters. In the policy table,
multiple ciphers, protocols or excluded ciphers must be separated by colons,
as attribute values may not contain whitespace or commas. When opportunistic
TLS handshakes fail, Postfix retries the connection with TLS disabled.
This allows mail delivery to sites with non-interoperable TLS
implementations.
encrypt
Mandatory TLS encryption. At this level
and higher, the optional “protocols” attribute overrides the main.cfsmtp_tls_mandatory_protocols parameter, the optional “ciphers” attribute
overrides the main.cfsmtp_tls_mandatory_ciphers parameter, the
optional “exclude” attribute (Postfix ≥ 2.6) overrides the main.cfsmtp_tls_mandatory_exclude_ciphers parameter, and the optional
“connection_reuse” attribute (Postfix ≥ 3.4) overrides the
main.cfsmtp_tls_connection_reuse parameter. In the policy table,
multiple ciphers, protocols or excluded ciphers must be separated by colons,
as attribute values may not contain whitespace or commas.
dane
Opportunistic DANE TLS. The TLS policy for the destination is
obtained via TLSA records in DNSSEC. If no TLSA records are found,
the effective security level used is may. If TLSA records are
found, but none are usable, the effective security level is encrypt. When usable
TLSA records are obtained for the remote SMTP server, the
server certificate must match the TLSA records. RFC 7672 (DANE)
TLS authentication and DNSSEC support is available with Postfix
2.11 and later. The optional “connection_reuse” attribute (Postfix
≥ 3.4) overrides the main.cfsmtp_tls_connection_reuse parameter.
When the effective security level used is may, the optional “ciphers”,
“exclude”, and “protocols” attributes (Postfix ≥ 2.6) override the
smtp_tls_ciphers“, “smtp_tls_exclude_ciphers“, and “smtp_tls_protocols
configuration parameters.
When the effective security level used is encrypt, the optional “ciphers”,
“exclude”, and “protocols” attributes (Postfix ≥ 2.6) override the
smtp_tls_mandatory_ciphers“, “smtp_tls_mandatory_exclude_ciphers“, and
smtp_tls_mandatory_protocols” configuration parameters.
dane-only
Mandatory DANE TLS. The TLS policy for the destination is
obtained via TLSA records in DNSSEC. If no TLSA records are found,
or none are usable, no connection is made to the server. When
usable TLSA records are obtained for the remote SMTP server, the
server certificate must match the TLSA records. RFC 7672 (DANE) TLS
authentication and DNSSEC support is available with Postfix 2.11
and later. The optional “ciphers”, “exclude”, and “protocols” attributes
(Postfix ≥ 2.6) override the “smtp_tls_mandatory_ciphers“,
smtp_tls_mandatory_exclude_ciphers“, and “smtp_tls_mandatory_protocols
configuration parameters. The optional “connection_reuse” attribute
(Postfix ≥ 3.4) overrides the main.cfsmtp_tls_connection_reuse parameter.
fingerprint
Certificate fingerprint
verification. Available with Postfix 2.5 and later. At this security
level, there are no trusted Certification Authorities. The certificate
trust chain, expiration date, … are not checked. Instead,
the optional “match” attribute, or else the main.cfsmtp_tls_fingerprint_cert_match parameter, lists the certificate
fingerprints or the public key fingerprint (Postfix 2.9 and later)
of the valid server certificate. The digest
algorithm used to calculate the fingerprint is selected by the
smtp_tls_fingerprint_digest parameter. Multiple fingerprints can
be combined with a “|” delimiter in a single match attribute, or multiple
match attributes can be employed. The “:” character is not used as a
delimiter as it occurs between each pair of fingerprint (hexadecimal)
digits. The optional “ciphers”, “exclude”, and “protocols” attributes
(Postfix ≥ 2.6) override the “smtp_tls_mandatory_ciphers“,
smtp_tls_mandatory_exclude_ciphers“, and “smtp_tls_mandatory_protocols
configuration parameters. The optional “connection_reuse” attribute
(Postfix ≥ 3.4) overrides the main.cfsmtp_tls_connection_reuse
parameter.
verify
Mandatory TLS verification. At this security
level, DNS MX lookups are trusted to be secure enough, and the name
verified in the server certificate is usually obtained indirectly via
unauthenticated DNS MX lookups. The optional “match” attribute overrides
the main.cfsmtp_tls_verify_cert_match parameter. In the policy table,
multiple match patterns and strategies must be separated by colons.
In practice explicit control over matching is more common with the
“secure” policy, described below. The optional “ciphers”, “exclude”,
and “protocols” attributes (Postfix ≥ 2.6) override the
smtp_tls_mandatory_ciphers“, “smtp_tls_mandatory_exclude_ciphers“, and
smtp_tls_mandatory_protocols” configuration parameters. The optional
“connection_reuse” attribute (Postfix ≥ 3.4) overrides the main.cfsmtp_tls_connection_reuse parameter.
secure
Secure-channel TLS. At this security level, DNS
MX lookups, though potentially used to determine the candidate next-hop
gateway IP addresses, are not trusted to be secure enough for TLS
peername verification. Instead, the default name verified in the server
certificate is obtained directly from the next-hop, or is explicitly
specified via the optional “match” attribute which overrides the
main.cfsmtp_tls_secure_cert_match parameter. In the policy table,
multiple match patterns and strategies must be separated by colons.
The match attribute is most useful when multiple domains are supported by
a common server: the policy entries for additional domains specify matching
rules for the primary domain certificate. While transport table overrides
that route the secondary domains to the primary nexthop also allow secure
verification, they risk delivery to the wrong destination when domains
change hands or are re-assigned to new gateways. With the “match”
attribute approach, routing is not perturbed, and mail is deferred if
verification of a new MX host fails. The optional “ciphers”, “exclude”,
and “protocols” attributes (Postfix ≥ 2.6) override the
smtp_tls_mandatory_ciphers“, “smtp_tls_mandatory_exclude_ciphers“, and
smtp_tls_mandatory_protocols” configuration parameters. The optional
“connection_reuse” attribute (Postfix ≥ 3.4) overrides the main.cfsmtp_tls_connection_reuse parameter.

Example:

/etc/postfix/main.cf:
    smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
    # Postfix 2.5 and later.
    #
    # The default digest is sha256 with Postfix ≥ 3.6 and
    # compatibility level ≥ 3.
    #
    smtp_tls_fingerprint_digest = sha256
/etc/postfix/tls_policy:
    example.edu                 none
    example.mil                 may
    example.gov                 encrypt protocols=TLSv1
    example.com                 verify ciphers=high
    example.net                 secure
    .example.net                secure match=.example.net:example.net
    [mail.example.org]:587      secure match=nexthop
    # Postfix 2.5 and later
    [thumb.example.org]          fingerprint
        match=b6:b4:72:34:e2:59:cd:...:c2:ca:63:0d:4d:cc:2c:7d:84:de:e6:2f
        match=51:e9:af:2e:1e:40:1f:...:64:0a:30:35:2d:09:16:31:5a:eb:82:76

Note: The “hostname” strategy if listed in a non-default
setting of smtp_tls_secure_cert_match or in the “match” attribute
in the policy table can render the “secure” level vulnerable to
DNS forgery. Do not use the “hostname” strategy for secure-channel
configurations in environments where DNS security is not assured.

This feature is available in Postfix 2.3 and later.


(default: see postconf -d output)

TLS protocols that the Postfix SMTP client will use with
opportunistic TLS encryption. In main.cf the values are separated by
whitespace, commas or colons. In the policy table “protocols” attribute
(see smtp_tls_policy_maps) the only valid separator is colon. An empty
value means allow all protocols.

The valid protocol names (see SSL_get_version(3)) are “SSLv2”,
“SSLv3”, “TLSv1”, “TLSv1.1”, “TLSv1.2” and “TLSv1.3”. Starting with
Postfix 3.6, the default value is “>=TLSv1”, which sets TLS 1.0 as
the lowest supported TLS protocol version (see below). Older releases
use the “!” exclusion syntax, also described below.

As of Postfix 3.6, the preferred way to limit the range of
acceptable protocols is to set the lowest acceptable TLS protocol
version and/or the highest acceptable TLS protocol version. To set the
lower bound include an element of the form: “>=version” where
version is either one of the TLS protocol names listed above,
or a hexadecimal number corresponding to the desired TLS protocol
version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.). For the upper
bound, use “<=version“. There must be no whitespace between
the “>=” or “<=” symbols and the protocol name or number.

Hexadecimal protocol numbers make it possible to specify protocol
bounds for TLS versions that are known to OpenSSL, but might not be
known to Postfix. They cannot be used with the legacy exclusion syntax.
Leading “0” or “0x” prefixes are supported, but not required.
Therefore, “301”, “0301”, “0x301” and “0x0301” are all equivalent to
“TLSv1”. Hexadecimal versions unknown to OpenSSL will fail to set the
upper or lower bound, and a warning will be logged. Hexadecimal
versions should only be used when Postfix is linked with some future
version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
yet support a symbolic name for that protocol version.

Hexadecimal example (Postfix ≥ 3.6):

# Allow only TLS 1.0 through (hypothetical) TLS 1.4, once supported
# in some future version of OpenSSL (presently a warning is logged).
smtp_tls_protocols = >=TLSv1, <=0305
# Allow only TLS 1.0 and up:
smtp_tls_protocols = >=0x0301

With Postfix < 3.6 there is no support for a minimum or maximum
version, and the protocol range is configured via protocol exclusions.
To require at least TLS 1.0, set “smtp_tls_protocols = !SSLv2, !SSLv3″.
Listing the protocols to include, rather than protocols to exclude, is
supported, but not recommended. The exclusion form more accurately
matches the underlying OpenSSL interface.

When using the exclusion syntax, take care to ensure that the range of
protocols advertised by an SSL/TLS client is contiguous. When a protocol
version is enabled, disabling any higher version implicitly disables all
versions above that higher version. Thus, for example:

smtp_tls_protocols = !SSLv2, !SSLv3, !TLSv1.1

also disables any protocols version higher than TLSv1.1 leaving
only “TLSv1” enabled.

Support for “TLSv1.3” was introduced in OpenSSL 1.1.1. Disabling
this protocol via “!TLSv1.3” is supported since Postfix 3.4 (or patch
releases ≥ 3.0.14, 3.1.10, 3.2.7 and 3.3.2).

Example:

# Preferred syntax with Postfix ≥ 3.6:
smtp_tls_protocols = >=TLSv1, <=TLSv1.3
# Legacy syntax:
smtp_tls_protocols = !SSLv2, !SSLv3

This feature is available in Postfix 2.6 and later.


(default: 9)

The verification depth for remote SMTP server certificates. A depth
of 1 is sufficient if the issuing CA is listed in a local CA file.

The default verification depth is 9 (the OpenSSL default) for
compatibility with earlier Postfix behavior. Prior to Postfix 2.5,
the default value was 5, but the limit was not actually enforced. If
you have set this to a lower non-default value, certificates with longer
trust chains may now fail to verify. Certificate chains with 1 or 2
CAs are common, deeper chains are more rare and any number between 5
and 9 should suffice in practice. You can choose a lower number if,
for example, you trust certificates directly signed by an issuing CA
but not any CAs it delegates to.

This feature is available in Postfix 2.2 and later.


(default: nexthop, dot-nexthop)

How the Postfix SMTP client verifies the server certificate
peername for the “secure” TLS security level. In a “secure” TLS policy table
($smtp_tls_policy_maps) entry the optional “match” attribute
overrides this main.cf setting.

This parameter specifies one or more patterns or strategies separated
by commas, whitespace or colons. In the policy table the only valid
separator is the colon character.

For a description of the pattern and strategy syntax see the
smtp_tls_verify_cert_match parameter. The “hostname” strategy should
be avoided in this context, as in the absence of a secure global DNS, using
the results of MX lookups in certificate verification is not immune to active
(man-in-the-middle) attacks on DNS.

Sample main.cf setting:

smtp_tls_secure_cert_match = nexthop

Sample policy table override:

example.net     secure match=example.com:.example.com
.example.net    secure match=example.com:.example.com

This feature is available in Postfix 2.3 and later.


(default: empty)

The default SMTP TLS security level for the Postfix SMTP client.
When a non-empty value is specified, this overrides the obsolete
parameters smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername;
when no value is specified for smtp_tls_enforce_peername or the obsolete
parameters, the default SMTP TLS security level is
none.

Specify one of the following security levels:

none
No TLS. TLS will not be used unless enabled for specific
destinations via smtp_tls_policy_maps.
may
Opportunistic TLS. Use TLS if this is supported by the remote
SMTP server, otherwise use plaintext. Since
sending in the clear is acceptable, demanding stronger than default TLS
security merely reduces interoperability.
The “smtp_tls_ciphers” and “smtp_tls_protocols” (Postfix ≥ 2.6)
configuration parameters provide control over the protocols and
cipher grade used with opportunistic TLS. With earlier releases the
opportunistic TLS cipher grade is always “export” and no protocols
are disabled.
When TLS handshakes fail, the connection is retried with TLS disabled.
This allows mail delivery to sites with non-interoperable TLS
implementations.
encrypt
Mandatory TLS encryption. Since a minimum
level of security is intended, it is reasonable to be specific about
sufficiently secure protocol versions and ciphers. At this security level
and higher, the main.cf parameters smtp_tls_mandatory_protocols and
smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
cipher grade which the administrator considers secure enough for
mandatory encrypted sessions. This security level is not an appropriate
default for systems delivering mail to the Internet.
dane
Opportunistic DANE TLS. At this security level, the TLS policy
for the destination is obtained via DNSSEC. For TLSA policy to be
in effect, the destination domain’s containing DNS zone must be
signed and the Postfix SMTP client’s operating system must be
configured to send its DNS queries to a recursive DNS nameserver
that is able to validate the signed records. Each MX host’s DNS
zone should also be signed, and should publish DANE TLSA (RFC 7672)
records that specify how that MX host’s TLS certificate is to be
verified. TLSA records do not preempt the normal SMTP MX host
selection algorithm, if some MX hosts support TLSA and others do
not, TLS security will vary from delivery to delivery. It is up
to the domain owner to configure their MX hosts and their DNS
sensibly. To configure the Postfix SMTP client for DNSSEC lookups
see the documentation for the smtp_dns_support_levelmain.cf
parameter. When DNSSEC-validated TLSA records are not found the
effective tls security level is “may”. When TLSA records are found,
but are all unusable the effective security level is “encrypt”. For
purposes of protocol and cipher selection, the “dane” security level
is treated like a “mandatory” TLS security level, and weak ciphers
and protocols are disabled. Since DANE authenticates server
certificates the “aNULL” cipher-suites are transparently excluded
at this level, no need to configure this manually. RFC 7672 (DANE)
TLS authentication is available with Postfix 2.11 and later.
dane-only
Mandatory DANE TLS. This is just like “dane” above, but DANE
TLSA authentication is required. There is no fallback to “may” or
“encrypt” when TLSA records are missing or unusable. RFC 7672
(DANE) TLS authentication is available with Postfix 2.11 and later.
fingerprint
Certificate fingerprint verification.
At this security level, there are no trusted Certification Authorities.
The certificate trust chain, expiration date, etc., are
not checked. Instead, the smtp_tls_fingerprint_cert_match
parameter lists the certificate fingerprint or public key fingerprint
(Postfix 2.9 and later) of the valid server certificate. The digest
algorithm used to calculate the fingerprint is selected by the
smtp_tls_fingerprint_digest parameter. Available with Postfix
2.5 and later.
verify
Mandatory TLS verification. At this security
level, DNS MX lookups are trusted to be secure enough, and the name
verified in the server certificate is usually obtained indirectly
via unauthenticated DNS MX lookups. The smtp_tls_verify_cert_match
parameter controls how the server name is verified. In practice explicit
control over matching is more common at the “secure” level, described
below. This security level is not an appropriate default for systems
delivering mail to the Internet.
secure
Secure-channel TLS. At this security level,
DNS MX lookups, though potentially used to determine the candidate
next-hop gateway IP addresses, are not trusted to be secure enough
for TLS peername verification. Instead, the default name verified in
the server certificate is obtained from the next-hop domain as specified
in the smtp_tls_secure_cert_match configuration parameter. The default
matching rule is that a server certificate matches when its name is equal
to or is a sub-domain of the nexthop domain. This security level is not
an appropriate default for systems delivering mail to the Internet.

Examples:

# No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
smtp_tls_security_level = none
# Opportunistic TLS.
smtp_tls_security_level = may
# Do not tweak opportunistic ciphers or protocols unless it is essential
# to do so (if a security vulnerability is found in the SSL library that
# can be mitigated by disabling a particular protocol or raising the
# cipher grade).
smtp_tls_ciphers = medium
smtp_tls_protocols = >=TLSv1
# Legacy (Postfix < 3.6) syntax:
smtp_tls_protocols = !SSLv2, !SSLv3
# Mandatory (high-grade) TLS encryption.
smtp_tls_security_level = encrypt
smtp_tls_mandatory_ciphers = high
# Authenticated TLS 1.2 or better matching the nexthop domain or a
# subdomain.
smtp_tls_security_level = secure
smtp_tls_mandatory_ciphers = high
smtp_tls_mandatory_protocols = >=TLSv1.2
smtp_tls_secure_cert_match = nexthop, dot-nexthop
# Certificate fingerprint verification (Postfix ≥ 2.5).
# The CA-less "fingerprint" security level only scales to a limited
# number of destinations. As a global default rather than a per-site
# setting, this is practical only when mail for all recipients is sent
# to a central mail hub.
relayhost = [mailhub.example.com]
smtp_tls_security_level = fingerprint
smtp_tls_mandatory_protocols = >=TLSv1.2
smtp_tls_mandatory_ciphers = high
smtp_tls_fingerprint_cert_match =
    3D:95:34:51:...:40:99:C0:C1
    EC:3B:2D:B0:...:A3:9D:72:F6

This feature is available in Postfix 2.3 and later.


(default: empty)

Optional name to send to the remote SMTP server in the TLS Server
Name Indication (SNI) extension. The SNI extension is always on when
DANE is used to authenticate the server, and in that case the SNI name
sent is the one required by RFC7672 and this parameter is ignored.

Some SMTP servers use the received SNI name to select an appropriate
certificate chain to present to the client. While this may improve
interoperability with such servers, it may reduce interoperability with
other servers that choose to abort the connection when they don’t have a
certificate chain configured for the requested name. Such servers
should select a default certificate chain and continue the handshake,
but some may not. Therefore, absent DANE, no SNI name is sent by
default.

The SNI name must be either a valid DNS hostname, or else one of the
special values hostname or nexthop, which select either the
remote hostname or the nexthop domain respectively. DNS names for SNI must be
in A-label (punycode) form. Invalid DNS names log a configuration error
warning and mail delivery is deferred.

Except when using a relayhost to forward all email, the only
sensible non-empty main.cf setting for this parameter is
hostname. Other non-empty values are only practical on a
per-destination basis via the servername attribute of the Postfix
TLS policy table. When
in doubt, leave this parameter empty, and configure per-destination SNI
as needed.

This feature is available in Postfix 3.4 and later.


(default: empty)

Name of the file containing the optional Postfix SMTP client
TLS session cache. Specify a database type that supports enumeration,
such as btree or sdbm; there is no need to support
concurrent access. The file is created if it does not exist. The smtp(8)
daemon does not use this parameter directly, rather the cache is
implemented indirectly in the tlsmgr(8) daemon. This means that
per-smtp-instance master.cf overrides of this parameter are not effective.
Note that each of the cache databases supported by tlsmgr(8) daemon:
$smtpd_tls_session_cache_database, $smtp_tls_session_cache_database
(and with Postfix 2.3 and later $lmtp_tls_session_cache_database), needs to
be stored separately. It is not at this time possible to store multiple
caches in a single database.

Note: dbm databases are not suitable. TLS
session objects are too large.

As of version 2.5, Postfix no longer uses root privileges when
opening this file. The file should now be stored under the Postfix-owned
data_directory. As a migration aid, an attempt to open the file
under a non-Postfix directory is redirected to the Postfix-owned
data_directory, and a warning is logged.

Example:

smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_scache

This feature is available in Postfix 2.2 and later.


(default: 3600s)

The expiration time of Postfix SMTP client TLS session cache
information. A cache cleanup is performed periodically
every $smtp_tls_session_cache_timeout seconds. As with
$smtp_tls_session_cache_database, this parameter is implemented in the
tlsmgr(8) daemon and therefore per-smtp-instance master.cf overrides
are not possible.

As of Postfix 2.11 this setting cannot exceed 100 days. If set
≤ 0, session caching is disabled. If set to a positive value
less than 2 minutes, the minimum value of 2 minutes is used instead.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.2 and later.


(default: empty)

Zero or more PEM-format files with trust-anchor certificates
and/or public keys. If the parameter is not empty the root CAs in
CAfile and CApath are no longer trusted. Rather, the Postfix SMTP
client will only trust certificate-chains signed by one of the
trust-anchors contained in the chosen files. The specified
trust-anchor certificates and public keys are not subject to
expiration, and need not be (self-signed) root CAs. They may, if
desired, be intermediate certificates. Therefore, these certificates
also may be found “in the middle” of the trust chain presented by
the remote SMTP server, and any untrusted issuing parent certificates
will be ignored. Specify a list of pathnames separated by comma
or whitespace.

Whether specified in main.cf, or on a per-destination basis,
the trust-anchor PEM file must be accessible to the Postfix SMTP
client in the chroot jail if applicable. The trust-anchor file
should contain only certificates and public keys, no private key
material, and must be readable by the non-privileged $mail_owner
user. This allows destinations to be bound to a set of specific
CAs or public keys without trusting the same CAs for all destinations.

The main.cf parameter supports single-purpose Postfix installations
that send mail to a fixed set of SMTP peers. At most sites, if
trust-anchor files are used at all, they will be specified on a
per-destination basis via the “tafile” attribute of the “verify”
and “secure” levels in smtp_tls_policy_maps.

The underlying mechanism is in support of RFC 7672 (DANE TLSA),
which defines mechanisms for an SMTP client MTA to securely determine
server TLS certificates via DNS.

If you want your trust anchors to be public keys, with OpenSSL
you can extract a single PEM public key from a PEM X.509 file
containing a single certificate, as follows:

$ openssl x509 -in cert.pem -out ta-key.pem -noout -pubkey

This feature is available in Postfix 2.11 and later.


(default: hostname)

How the Postfix SMTP client verifies the server certificate
peername for the
“verify” TLS security level. In a “verify” TLS policy table
($smtp_tls_policy_maps) entry the optional “match” attribute
overrides this main.cf setting.

This parameter specifies one or more patterns or strategies separated
by commas, whitespace or colons. In the policy table the only valid
separator is the colon character.

Patterns specify domain names, or domain name suffixes:

example.com
Match the example.com domain,
i.e. one of the names in the server certificate must be example.com.
Upper and lower case distinctions are ignored.
.example.com
Match subdomains of the example.com domain, i.e. match
a name in the server certificate that consists of a non-zero number of
labels followed by a .example.com suffix. Case distinctions are
ignored.

Strategies specify a transformation from the next-hop domain
to the expected name in the server certificate:

nexthop
Match against the next-hop domain, which is either the recipient
domain, or the transport next-hop configured for the domain stripped of
any optional socket type prefix, enclosing square brackets and trailing
port. When MX lookups are not suppressed, this is the original nexthop
domain prior to the MX lookup, not the result of the MX lookup. For
LMTP delivery via UNIX-domain sockets, the verified next-hop name is
$myhostname. This strategy is suitable for use with the “secure”
policy. Case is ignored.
dot-nexthop
As above, but match server certificate names that are subdomains
of the next-hop domain. Case is ignored.
hostname
Match against the hostname of the server, often
obtained via an unauthenticated DNS MX lookup. For LMTP delivery via
UNIX-domain sockets, the verified name is $myhostname. This matches
the verification strategy of the “MUST” keyword in the obsolete
smtp_tls_per_site table, and is suitable for use with the “verify”
security level. When the next-hop name is enclosed in square brackets
to suppress MX lookups, the “hostname” strategy is the same as the
“nexthop” strategy. Case is ignored.

Sample main.cf setting:

smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

Sample policy table override:

example.com     verify  match=hostname:nexthop
.example.com    verify  match=example.com:.example.com:hostname

This feature is available in Postfix 2.3 and later.


(default: no)

Request that the Postfix SMTP client connects using the
SUBMISSIONS/SMTPS protocol instead of using the STARTTLS command.

This mode requires “smtp_tls_security_level = encrypt” or
stronger.

Example: deliver all remote mail via a provider’s server
“mail.example.com”.

/etc/postfix/main.cf:
    # Client-side SMTPS requires "encrypt" or stronger.
    smtp_tls_security_level = encrypt
    smtp_tls_wrappermode = yes
    # The [] suppress MX lookups.
    relayhost = [mail.example.com]:465

More examples are in TLS_README, including examples for older
Postfix versions.

This feature is available in Postfix 3.0 and later.


(default: no)

Opportunistic mode: use TLS when a remote SMTP server announces
STARTTLS support, otherwise send the mail in the clear. Beware:
some SMTP servers offer STARTTLS even if it is not configured. With
Postfix < 2.3, if the TLS handshake fails, and no other server is
available, delivery is deferred and mail stays in the queue. If this
is a concern for you, use the smtp_tls_per_site feature instead.

This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_security_level instead.


(default: 300s)

The Postfix SMTP client time limit for sending the XFORWARD command,
and for receiving the remote SMTP server response.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: $authorized_verp_clients)

What remote SMTP clients are allowed to specify the XVERP command.
This command requests that mail be delivered one recipient at a
time with a per recipient return address.

By default, no clients are allowed to specify XVERP.

This parameter was renamed with Postfix version 2.1. The default value
is backwards compatible with Postfix version 2.0.

Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it), “/file/name” or “type:table” patterns. A “/file/name”
pattern is replaced by its contents; a “type:table” lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored). Continue long lines by starting the next line
with whitespace. Specify “!pattern” to exclude an address or network
block from the list. The form “!/file/name” is supported only in
Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside
[] in the smtpd_authorized_verp_clients value, and in
files specified with “/file/name”. IP version 6 addresses contain
the “:” character, and would otherwise be confused with a “type:table
pattern.


(default: empty)

What remote SMTP clients are allowed to use the XCLIENT feature. This
command overrides remote SMTP client information that is used for access
control. Typical use is for SMTP-based content filters, fetchmail-like
programs, or SMTP server access rule testing. See the XCLIENT_README
document for details.

This feature is available in Postfix 2.1 and later.

By default, no clients are allowed to specify XCLIENT.

Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it), “/file/name” or “type:table” patterns. A “/file/name”
pattern is replaced by its contents; a “type:table” lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored). Continue long lines by starting the next line
with whitespace. Specify “!pattern” to exclude an address or network
block from the list. The form “!/file/name” is supported only in
Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside
[] in the smtpd_authorized_xclient_hosts value, and in
files specified with “/file/name”. IP version 6 addresses contain
the “:” character, and would otherwise be confused with a “type:table
pattern.


(default: empty)

What remote SMTP clients are allowed to use the XFORWARD feature. This
command forwards information that is used to improve logging after
SMTP-based content filters. See the XFORWARD_README document for
details.

This feature is available in Postfix 2.1 and later.

By default, no clients are allowed to specify XFORWARD.

Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it), “/file/name” or “type:table” patterns. A “/file/name”
pattern is replaced by its contents; a “type:table” lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored). Continue long lines by starting the next line
with whitespace. Specify “!pattern” to exclude an address or network
block from the list. The form “!/file/name” is supported only in
Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside
[] in the smtpd_authorized_xforward_hosts value, and in
files specified with “/file/name”. IP version 6 addresses contain
the “:” character, and would otherwise be confused with a “type:table
pattern.


(default: $myhostname ESMTP $mail_name)

The text that follows the 220 status code in the SMTP greeting
banner. Some people like to see the mail version advertised. By
default, Postfix shows no version.

You MUST specify $myhostname at the start of the text. This is
required by the SMTP protocol.

Example:

smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

(default: 0)

The maximal number of AUTH commands that any client is allowed to
send to this service per time unit, regardless of whether or not
Postfix actually accepts those commands. The time unit is specified
with the anvil_rate_time_unit configuration parameter.

By default, there is no limit on the number of AUTH commands that a
client may send.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.

This feature is available in Postfix 3.1 and later.


(default: 50)

How many simultaneous connections any client is allowed to
make to this service. By default, the limit is set to half
the default process limit value.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.


(default: 0)

The maximal number of connection attempts any client is allowed to
make to this service per time unit. The time unit is specified
with the anvil_rate_time_unit configuration parameter.

By default, a client can make as many connections per time unit as
Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_connection_rate_limit = 1000

(default: $mynetworks)

Clients that are excluded from smtpd_client_*_count/rate_limit
restrictions. See the mynetworks parameter
description for the parameter value syntax.

By default, clients in trusted networks are excluded. Specify a
list of network blocks, hostnames or .domain names (the initial
dot causes the domain to match any name below it).

Note: IP version 6 address information must be specified inside
[] in the smtpd_client_event_limit_exceptions value, and
in files specified with “/file/name”. IP version 6 addresses
contain the “:” character, and would otherwise be confused with a
type:table” pattern.

Pattern matching of domain names is controlled by the presence
or absence of “smtpd_client_event_limit_exceptions” in the
parent_domain_matches_subdomains parameter value (Postfix 3.0 and
later).

This feature is available in Postfix 2.2 and later.


(default: 0)

The maximal number of message delivery requests that any client is
allowed to make to this service per time unit, regardless of whether
or not Postfix actually accepts those messages. The time unit is
specified with the anvil_rate_time_unit configuration parameter.

By default, a client can send as many message delivery requests
per time unit as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_message_rate_limit = 1000

(default: 0)

The maximal number of new (i.e., uncached) TLS sessions that a
remote SMTP client is allowed to negotiate with this service per
time unit. The time unit is specified with the anvil_rate_time_unit
configuration parameter.

By default, a remote SMTP client can negotiate as many new TLS
sessions per time unit as Postfix can accept.

To disable this feature, specify a limit of 0. Otherwise, specify
a limit that is at least the per-client concurrent session limit,
or else legitimate client sessions may be rejected.

WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.

This feature is available in Postfix 2.3 and later.

Example:

smtpd_client_new_tls_session_rate_limit = 100

(default: no)

Enable logging of the remote SMTP client port in addition to
the hostname and IP address. The logging format is “host[address]:port”.

This feature is available in Postfix 2.5 and later.


(default: 0)

The maximal number of recipient addresses that any client is allowed
to send to this service per time unit, regardless of whether or not
Postfix actually accepts those recipients. The time unit is specified
with the anvil_rate_time_unit configuration parameter.

By default, a client can send as many recipient addresses per time
unit as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_recipient_rate_limit = 1000

(default: empty)

Optional restrictions that the Postfix SMTP server applies in the
context of a client connection request.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

The default is to allow all connection requests.

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.

The following restrictions are specific to client hostname or
client network address information.

type:table
By default use the remote SMTP client certificate fingerprint
or the public key
fingerprint (Postfix 2.9 and later) as the lookup key for the specified
access(5) database; with Postfix version 2.2, also require that the
remote SMTP client certificate is verified successfully.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5). This feature requires “smtpd_tls_ask_ccert
= yes” and is available with Postfix version
2.2 and later.
The default algorithm is sha256 with Postfix ≥ 3.6
and the compatibility_level set to 3.6 or higher. With Postfix
≤ 3.5, the default algorithm is md5. The best-practice
algorithm is now sha256. Recent advances in hash function
cryptanalysis have led to md5 and sha1 being deprecated in favor of
sha256. However, as long as there are no known “second pre-image”
attacks against the older algorithms, their use in this context, though
not recommended, is still likely safe.
Alternatively, check_ccert_access accepts an explicit search
order (Postfix 3.5 and later). The default search order as described
above corresponds with:
check_ccert_access { type:table, { search_order = cert_fingerprint,
pubkey_fingerprint } }
The commas are optional.
type:table
Search the specified access database for the client hostname,
parent domains, client IP address, or networks obtained by stripping
least significant octets. See the access(5) manual page for details.
type:table
Search the specified access(5) database for the IP addresses for the
client hostname, and execute the corresponding action. Note: a result
of “OK” is not allowed for safety reasons. Instead, use DUNNO in order
to exclude specific hosts from denylists. This feature is available
in Postfix 3.0 and later.
type:table
Search the specified access(5) database for the MX hosts for the
client hostname, and execute the corresponding action. If no MX
record is found, look up A or AAAA records, just like the Postfix
SMTP client would. Note: a result
of “OK” is not allowed for safety reasons. Instead, use DUNNO in order
to exclude specific hosts from denylists. This feature is available
in Postfix 2.7 and later.
type:table
Search the specified access(5) database for the DNS servers for
the client hostname, and execute the corresponding action. Note: a
result of “OK” is not allowed for safety reasons. Instead, use DUNNO
in order to exclude specific hosts from denylists. This feature is
available in Postfix 2.7 and later.
type:table
Search the specified access database for the unverified reverse
client hostname, parent domains, client IP address, or networks
obtained by stripping least significant octets. See the access(5)
manual page for details. Note: a result of “OK” is not allowed for
safety reasons. Instead, use DUNNO in order to exclude specific
hosts from denylists. This feature is available in Postfix 2.6
and later.
type:table
Search the specified access(5) database for the IP addresses for the
unverified reverse client hostname, and execute the corresponding
action. Note: a result of “OK” is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from denylists.
This feature is available in Postfix 3.0 and later.
type:table
Search the specified access(5) database for the MX hosts for the
unverified reverse client hostname, and execute the corresponding
action. If no MX record is found, look up A or AAAA records, just
like the Postfix SMTP client would.
Note: a result of “OK” is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from denylists.
This feature is available in Postfix 2.7 and later.
type:table
Search the specified access(5) database for the DNS servers for
the unverified reverse client hostname, and execute the corresponding
action. Note: a result of “OK” is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from denylists.
This feature is available in Postfix 2.7 and later.
type:table
Use the remote SMTP client SASL user name as the lookup key for
the specified access(5) database. The lookup key has the form
“username@domainname” when the smtpd_sasl_local_domain parameter
value is non-empty. Unlike the check_client_access feature,
check_sasl_access does not perform matches of parent domains or IP
subnet ranges. This feature is available with Postfix version 2.11
and later.
Permit the request when the client IP address matches
$inet_interfaces.
Permit the request when the client IP address matches any
network or network address listed in $mynetworks.
Permit the request when the client is successfully
authenticated via the RFC 4954 (AUTH) protocol.
Permit the request when the remote SMTP client certificate is
verified successfully. This option must be used only if a special
CA issues the certificates and only this CA is listed as a trusted
CA. Otherwise, clients with a third-party certificate would also
be allowed to relay. Specify “tls_append_default_CA = no” when the
trusted CA is specified with smtpd_tls_CAfile or smtpd_tls_CApath,
to prevent Postfix from appending the system-supplied default CAs.
This feature requires “smtpd_tls_ask_ccert = yes” and is available
with Postfix version 2.2 and later.
Permit the request when the remote SMTP client certificate
fingerprint or public key fingerprint (Postfix 2.9 and later) is
listed in $relay_clientcerts.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5). This feature requires “smtpd_tls_ask_ccert
= yes” and is available with Postfix version 2.2 and later.
The default algorithm is sha256 with Postfix ≥ 3.6
and the compatibility_level set to 3.6 or higher. With Postfix
≤ 3.5, the default algorithm is md5. The best-practice
algorithm is now sha256. Recent advances in hash function
cryptanalysis have led to md5 and sha1 being deprecated in favor of
sha256. However, as long as there are no known “second pre-image”
attacks against the older algorithms, their use in this context, though
not recommended, is still likely safe.
Reject the request when the reversed client network address is
listed with the A record “d.d.d.d” under rbl_domain
(Postfix version 2.1 and later only). Each “d” is a number,
or a pattern inside “[]” that contains one or more “;”-separated
numbers or number..number ranges (Postfix version 2.8 and later).
If no “=d.d.d.d” is specified, reject the request when the
reversed client network address is listed with any A record under
rbl_domain.
The maps_rbl_reject_code parameter specifies the response code for
rejected requests (default: 554), the default_rbl_reply parameter
specifies the default server reply, and the rbl_reply_maps parameter
specifies tables with server replies indexed by rbl_domain.
This feature is available in Postfix 2.0 and later.
Accept the request when the reversed client network address is
listed with the A record “d.d.d.d” under dnswl_domain.
Each “d” is a number, or a pattern inside “[]” that contains
one or more “;”-separated numbers or number..number ranges.
If no “=d.d.d.d” is specified, accept the request when the
reversed client network address is listed with any A record under
dnswl_domain.
For safety, permit_dnswl_client is silently
ignored when it would override reject_unauth_destination. The
result is DEFER_IF_REJECT when allowlist lookup fails. This feature
is available in Postfix 2.8 and later.
Reject the request when the client hostname is listed with the
A record “d.d.d.d” under rbl_domain (Postfix version
2.1 and later only). Each “d” is a number, or a pattern
inside “[]” that contains one or more “;”-separated numbers or
number..number ranges (Postfix version 2.8 and later). If no
=d.d.d.d” is specified, reject the request when the client
hostname is listed with
any A record under rbl_domain. See the reject_rbl_client
description above for additional RBL related configuration parameters.
This feature is available in Postfix 2.0 and later; with Postfix
version 2.8 and later, reject_rhsbl_reverse_client will usually
produce better results.
Accept the request when the client hostname is listed with the
A record “d.d.d.d” under rhswl_domain. Each “d
is a number, or a pattern inside “[]” that contains one or more
“;”-separated numbers or number..number ranges. If no
=d.d.d.d” is specified, accept the request when the client
hostname is listed with any A record under rhswl_domain.

Caution: client name allowlisting is fragile, since the client
name lookup can fail due to temporary outages. Client name
allowlisting should be used only to reduce false positives in e.g.
DNS-based blocklists, and not for making access rule exceptions.

For safety, permit_rhswl_client is silently ignored when it
would override reject_unauth_destination. The result is DEFER_IF_REJECT
when allowlist lookup fails. This feature is available in Postfix
2.8 and later.
Reject the request when the unverified reverse client hostname
is listed with the A record “d.d.d.d” under rbl_domain.
Each “d” is a number, or a pattern inside “[]” that contains
one or more “;”-separated numbers or number..number ranges.
If no “=d.d.d.d” is specified, reject the request when the
unverified reverse client hostname is listed with any A record under
rbl_domain. See the reject_rbl_client description above for
additional RBL related configuration parameters. This feature is
available in Postfix 2.8 and later.
(with Postfix < 2.3: reject_unknown_client)
Reject the request when 1) the client IP address->name mapping
fails, or 2) the name->address mapping fails, or 3) the name->address
mapping does not match the client IP address.
This is a
stronger restriction than the reject_unknown_reverse_client_hostname
feature, which triggers only under condition 1) above.
The
unknown_client_reject_code parameter specifies the response code
for rejected requests (default: 450). The reply is always 450 in
case the address->name or name->address lookup failed due to
a temporary problem.
Reject the request when the client IP address has no address->name
mapping.
This is a weaker restriction than the
reject_unknown_client_hostname feature, which requires not only
that the address->name and name->address mappings exist, but
also that the two mappings reproduce the client IP address.
The unknown_client_reject_code parameter specifies the response
code for rejected requests (default: 450). The reply is always 450
in case the address->name lookup failed due to a temporary
problem.
This feature is available in Postfix 2.3 and
later.

In addition, you can use any of the following restrictions. These restrictions are applicable in
any SMTP command context.

Query the specified policy server. See the SMTPD_POLICY_README
document for details. This feature is available in Postfix 2.1
and later.
Defer the request. The client is told to try again later. This
restriction is useful at the end of a restriction list, to make
the default policy explicit.
The defer_code parameter specifies
the SMTP server reply code (default: 450).
Defer the request if some later restriction would result in an
explicit or implicit PERMIT action. This is useful when a denylisting
feature fails due to a temporary problem. This feature is available
in Postfix version 2.1 and later.
Defer the request if some later restriction would result in a
REJECT action. This is useful when an allowlisting feature fails
due to a temporary problem. This feature is available in Postfix
version 2.1 and later.
Permit the request. This restriction is useful at the end of
a restriction list, to make the default policy explicit.
Reject the request when the envelope sender is the null address,
and the message has multiple envelope recipients. This usage has
rare but legitimate applications: under certain conditions,
multi-recipient mail that was posted with the DSN option NOTIFY=NEVER
may be forwarded with the null sender address.

Note: this restriction can only work reliably
when used in smtpd_data_restrictions or
smtpd_end_of_data_restrictions, because the total number of
recipients is not known at an earlier stage of the SMTP conversation.
Use at the RCPT stage will only reject the second etc. recipient.

The multi_recipient_bounce_reject_code parameter specifies the
response code for rejected requests (default: 550). This feature
is available in Postfix 2.1 and later.
Reject the request when the connection is not encrypted. This
restriction should not be used before the client has had a chance
to negotiate encryption with the AUTH or STARTTLS commands.

The plaintext_reject_code parameter specifies the response
code for rejected requests (default: 450). This feature is available
in Postfix 2.3 and later.
Reject the request when the client sends SMTP commands ahead
of time where it is not allowed, or when the client sends SMTP
commands ahead of time without knowing that Postfix actually supports
ESMTP command pipelining. This stops mail from bulk mail software
that improperly uses ESMTP command pipelining in order to speed up
deliveries.

With Postfix 2.6 and later, the SMTP server sets a per-session
flag whenever it detects illegal pipelining, including pipelined
HELO or EHLO commands. The reject_unauth_pipelining feature simply
tests whether the flag was set at any point in time during the
session.

With older Postfix versions, reject_unauth_pipelining checks
the current status of the input read queue, and its usage is not
recommended in contexts other than smtpd_data_restrictions.
Reject the request. This restriction is useful at the end of
a restriction list, to make the default policy explicit. The
reject_code configuration parameter specifies the response code for
rejected requests (default: 554).
Pause for the specified number of seconds and proceed with
the next restriction in the list, if any. This may stop zombie
mail when used as:

/etc/postfix/main.cf:
    smtpd_client_restrictions =
        sleep 1, reject_unauth_pipeliningsmtpd_delay_reject = no

This feature is available in Postfix 2.3.

A safety net for testing. When “warn_if_reject” is placed
before a reject-type restriction, access table query, or
check_policy_service query, this logs a “reject_warning” message
instead of rejecting a request (when a reject-type restriction fails
due to a temporary error, this logs a “reject_warning” message for
any implicit “defer_if_permit” actions that would normally prevent
mail from being accepted by some later access restriction). This
feature has no effect on defer_if_reject restrictions.

Other restrictions that are valid in this context:

Example:

smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

(default: empty)

A mechanism to transform commands from remote SMTP clients.
This is a last-resort tool to work around client commands that break
interoperability with the Postfix SMTP server. Other uses involve
fault injection to test Postfix’s handling of invalid commands.

Specify the name of a “type:table” lookup table. The search
string is the SMTP command as received from the remote SMTP client,
except that initial whitespace and the trailing <CR><LF>
are removed. The result value is executed by the Postfix SMTP
server.

There is no need to use smtpd_command_filter for the following
cases:

Examples of problems that can be solved with the smtpd_command_filter
feature:

/etc/postfix/main.cf:
    smtpd_command_filter = pcre:/etc/postfix/command_filter
/etc/postfix/command_filter:
    # Work around clients that send malformed HELO commands.
    /^HELOs*$/ HELO domain.invalid
    # Work around clients that send empty lines.
    /^s*$/     NOOP
    # Work around clients that send RCPT TO:<'user@domain'>.
    # WARNING: do not lose the parameters that follow the address.
    /^(RCPTs TO:s*<)'([^[:space:]] )'(>.*)/     $1$2$3
    # Append XVERP to MAIL FROM commands to request VERP-style delivery.
    # See VERP_README for more information on how to use Postfix VERP.
    /^(MAILs FROM:s*<listname@example.com>.*)/   $1 XVERP
    # Bounce-never mail sink. Use notify_classes=bounce,resource,software
    # to send bounced mail to the postmaster (with message body removed).
    /^(RCPTs TO:s*<.*>.*)s NOTIFY=S (.*)/     $1 NOTIFY=NEVER$2
    /^(RCPTs TO:.*)/                             $1 NOTIFY=NEVER

This feature is available in Postfix 2.7.


(default: empty)

Optional access restrictions that the Postfix SMTP server applies
in the context of the SMTP DATA command.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

This feature is available in Postfix 2.0 and later.

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.

The following restrictions are valid in this context:

Examples:

smtpd_data_restrictions = reject_unauth_pipeliningsmtpd_data_restrictions = reject_multi_recipient_bounce

(default: yes)

Postpone the start of an SMTP mail transaction until a valid
RCPT TO command is received. Specify “no” to create a mail transaction
as soon as the Postfix SMTP server receives a valid MAIL FROM
command.

With sites that reject lots of mail, the default setting reduces
the use of
disk, CPU and memory resources. The downside is that rejected
recipients are logged with NOQUEUE instead of a mail transaction
ID. This complicates the logfile analysis of multi-recipient mail.

This feature is available in Postfix 2.3 and later.


(default: yes)

Wait until the RCPT TO command before evaluating
$smtpd_client_restrictions, $smtpd_helo_restrictions and
$smtpd_sender_restrictions, or wait until the ETRN command before
evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.

This feature is turned on by default because some clients apparently
mis-behave when the Postfix SMTP server rejects commands before
RCPT TO.

The default setting has one major benefit: it allows Postfix to log
recipient address information when rejecting a client name/address
or sender address, so that it is possible to find out whose mail
is being rejected.


(default: empty)

Lookup tables, indexed by the remote SMTP client address, with
case insensitive lists of EHLO keywords (pipelining, starttls, auth,
etc.) that the Postfix SMTP server will not send in the EHLO response
to a
remote SMTP client. See smtpd_discard_ehlo_keywords for details.
The tables are not searched by hostname for robustness reasons.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

This feature is available in Postfix 2.2 and later.


(default: empty)

A case insensitive list of EHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix SMTP server will not send in the EHLO
response
to a remote SMTP client.

This feature is available in Postfix 2.2 and later.

Notes:


(default: empty)

Optional filter for Postfix SMTP server DNS lookup results.
See smtp_dns_reply_filter for details including an example.

This feature is available in Postfix 3.0 and later.


(default: empty)

Optional access restrictions that the Postfix SMTP server
applies in the context of the SMTP END-OF-DATA command.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

This feature is available in Postfix 2.2 and later.

See smtpd_data_restrictions for details and limitations.


(default: no)

Mandatory TLS: announce STARTTLS support to remote SMTP clients,
and require that clients use TLS encryption. According to RFC 2487
this MUST NOT be applied in case of a publicly-referenced SMTP
server. This option is therefore off by default.

Note 1: “smtpd_enforce_tls = yes” implies “smtpd_tls_auth_only = yes”.

Note 2: when invoked via “sendmail -bs“, Postfix will never offer
STARTTLS due to insufficient privileges to access the server private
key. This is intended behavior.

This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtpd_tls_security_level instead.


(default: 1s)

With Postfix version 2.1 and later: the SMTP server response delay after
a client has made more than $smtpd_soft_error_limit errors, and
fewer than $smtpd_hard_error_limit errors, without delivering mail.

With Postfix version 2.0 and earlier: the SMTP server delay
before sending a reject (4xx or 5xx) response, when the client has
made fewer than $smtpd_soft_error_limit errors without delivering
mail. When the client has made $smtpd_soft_error_limit or more errors,
delay all responses with the larger of (number of errors) seconds
or $smtpd_error_sleep_time.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

Optional restrictions that the Postfix SMTP server applies in the
context of a client ETRN command.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

The Postfix ETRN implementation accepts only destinations that are
eligible for the Postfix “fast flush” service. See the ETRN_README
file for details.

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.

The following restrictions are specific to the domain name information
received with the ETRN command.

type:table
Search the specified access database for the ETRN domain name
or its parent domains. See the access(5) manual page for details.

Other restrictions that are valid in this context:

Example:

smtpd_etrn_restrictions = permit_mynetworks, reject

(default: see “postconf -d” output)

What characters are allowed in $name expansions of RBL reply
templates. Characters not in the allowed set are replaced by “_”.
Use C like escapes to specify special characters such as whitespace.

The smtpd_expansion_filter value is not subject to Postfix configuration
parameter $name expansion.

This feature is available in Postfix 2.0 and later.


(default: CONNECT GET POST regexp:{{/^[^A-Z]/ Bogus}})

List of commands that cause the Postfix SMTP server to immediately
terminate the session with a 221 code. This can be used to disconnect
clients that obviously attempt to abuse the system. In addition to the
commands listed in this parameter, commands that follow the “Label:”
format of message headers will also cause a disconnect. With Postfix
versions 3.6 and earlier, the default value is “CONNECT GET POST”.

This feature is available in Postfix 2.2 and later.

Support for inline regular expressions was added in Postfix version
3.7. See regexp_table(5) for a description of the syntax and features.


(default: normal: 20, overload: 1)

The maximal number of errors a remote SMTP client is allowed to
make without delivering mail. The Postfix SMTP server disconnects
when the limit is reached. Normally the default limit is 20, but
it changes under overload to just 1. With Postfix 2.5 and earlier,
the SMTP server always allows up to 20 errors by default.
Valid values are greater than zero.


(default: no)

Require that a remote SMTP client introduces itself with the HELO
or EHLO command before sending the MAIL command or other commands
that require EHLO negotiation.

Example:

smtpd_helo_required = yes

(default: empty)

Optional restrictions that the Postfix SMTP server applies in the
context of a client HELO command.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

The default is to permit everything.

Note: specify “smtpd_helo_required = yes” to fully enforce this
restriction (without “smtpd_helo_required = yes”, a client can
simply skip smtpd_helo_restrictions by not sending HELO or EHLO).

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.

The following restrictions are specific to the hostname information
received with the HELO or EHLO command.

type:table
Search the specified access(5) database for the HELO or EHLO
hostname or parent domains, and execute the corresponding action.
Note: specify “smtpd_helo_required = yes” to fully enforce this
restriction (without “smtpd_helo_required = yes”, a client can
simply skip check_helo_access by not sending HELO or EHLO).
type:table
Search the specified access(5) database for the IP addresses for
the HELO or EHLO hostname, and execute the corresponding action.
Note 1: a result of “OK” is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from denylists. Note
2: specify “smtpd_helo_required = yes” to fully enforce this
restriction (without “smtpd_helo_required = yes”, a client can
simply skip check_helo_a_access by not sending HELO or EHLO). This
feature is available in Postfix 3.0 and later.
type:table
Search the specified access(5) database for the MX hosts for
the HELO or EHLO hostname, and execute the corresponding action.
If no MX record is found, look up A or AAAA records, just like the
Postfix SMTP client would.
Note 1: a result of “OK” is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from denylists. Note
2: specify “smtpd_helo_required = yes” to fully enforce this
restriction (without “smtpd_helo_required = yes”, a client can
simply skip check_helo_mx_access by not sending HELO or EHLO). This
feature is available in Postfix 2.1 and later.
type:table
Search the specified access(5) database for the DNS servers
for the HELO or EHLO hostname, and execute the corresponding action.
Note 1: a result of “OK” is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from denylists. Note
2: specify “smtpd_helo_required = yes” to fully enforce this
restriction (without “smtpd_helo_required = yes”, a client can
simply skip check_helo_ns_access by not sending HELO or EHLO). This
feature is available in Postfix 2.1 and later.
(with Postfix < 2.3: reject_invalid_hostname)
Reject the request when the HELO or EHLO hostname is malformed.
Note: specify “smtpd_helo_required = yes” to fully enforce
this restriction (without “smtpd_helo_required = yes”, a client can simply
skip reject_invalid_helo_hostname by not sending HELO or EHLO).

The invalid_hostname_reject_code specifies the response code
for rejected requests (default: 501).
(with Postfix < 2.3: reject_non_fqdn_hostname)
Reject the request when the HELO or EHLO hostname is not in
fully-qualified domain or address literal form, as required by the
RFC. Note: specify
smtpd_helo_required = yes” to fully enforce this restriction
(without “smtpd_helo_required = yes”, a client can simply skip
reject_non_fqdn_helo_hostname by not sending HELO or EHLO).
The non_fqdn_reject_code parameter specifies the response code for
rejected requests (default: 504).
Reject the request when the HELO or EHLO hostname is
listed with the A record “d.d.d.d” under rbl_domain
(Postfix version 2.1 and later only). Each “d” is a number,
or a pattern inside “[]” that contains one or more “;”-separated
numbers or number..number ranges (Postfix version 2.8 and later).
If no “=d.d.d.d” is
specified, reject the request when the HELO or EHLO hostname is
listed with any A record under rbl_domain. See the
reject_rbl_client description for additional RBL related configuration
parameters. Note: specify “smtpd_helo_required = yes” to fully
enforce this restriction (without “smtpd_helo_required = yes”, a
client can simply skip reject_rhsbl_helo by not sending HELO or
EHLO). This feature is available in Postfix 2.0
and later.
(with Postfix < 2.3: reject_unknown_hostname)
Reject the request when the HELO or EHLO hostname has no DNS A
or MX record.
The reply is specified with the
unknown_hostname_reject_code parameter (default: 450) or
unknown_helo_hostname_tempfail_action (default: defer_if_permit).
See the respective parameter descriptions for details.
Note: specify “smtpd_helo_required = yes” to fully
enforce this restriction (without “smtpd_helo_required = yes”, a
client can simply skip reject_unknown_helo_hostname by not sending
HELO or EHLO).

Other restrictions that are valid in this context:

Examples:

smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostnamesmtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

(default: 100)

The maximal number of lines in the Postfix SMTP server command history
before it is flushed upon receipt of EHLO, RSET, or end of DATA.


(default: normal: 100, overload: 1)

The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote
SMTP client can send before the Postfix SMTP server starts to
increment the error counter with each junk command. The junk
command count is reset after mail is delivered. See also the
smtpd_error_sleep_time and smtpd_soft_error_limit configuration
parameters. Normally the default limit is 100, but it changes under
overload to just 1. With Postfix 2.5 and earlier, the SMTP server
always allows up to 100 junk commands by default.


(default: empty)

Enable logging of the named “permit” actions in SMTP server
access lists (by default, the SMTP server logs “reject” actions but
not “permit” actions). This feature does not affect conditional
actions such as “defer_if_permit“.

Specify a list of “permit” action names, “/file/name” or
type:table” patterns, separated by commas and/or whitespace. The
list is matched left to right, and the search stops on the first
match. A “/file/name” pattern is replaced by its contents; a
type:table” lookup table is matched when a name matches a lookup
key (the lookup result is ignored). Continue long lines by starting
the next line with whitespace. Specify “!pattern” to exclude a name
from the list.

Examples:

/etc/postfix/main.cf:
    # Log all "permit" actions.
    smtpd_log_access_permit_actions = static:all
/etc/postfix/main.cf:
    # Log "permit_dnswl_client" only.
    smtpd_log_access_permit_actions = permit_dnswl_client

This feature is available in Postfix 2.10 and later.


(default: empty)

Lookup tables with Milter settings per remote SMTP client IP
address. The lookup result overrides the smtpd_milters setting,
and has the same syntax.

Note: lookup tables cannot return empty responses. Specify a
lookup result of DISABLE (case does not matter) to indicate that
Milter support should be disabled.

Example to disable Milters for local clients:

/etc/postfix/main.cf:
    smtpd_milter_maps = cidr:/etc/postfix/smtpd_milter_map
    smtpd_milters = inet:host:port, { inet:host:port, ... }, ...
/etc/postfix/smtpd_milter_map:
    # Disable Milters for local clients.
    127.0.0.0/8    DISABLE
    192.168.0.0/16 DISABLE
    ::/64          DISABLE
    2001:db8::/32  DISABLE

This feature is available in Postfix 3.2 and later.


(default: empty)

A list of Milter (mail filter) applications for new mail that
arrives via the Postfix smtpd(8) server. Specify space or comma as
separator. See the MILTER_README document for details.

This feature is available in Postfix 2.3 and later.


(default: 500)

The minimum plaintext data transfer rate in bytes/second for
DATA and BDAT requests, when deadlines are enabled with
smtpd_per_request_deadline. After a read operation transfers N
plaintext message bytes (possibly after TLS decryption), and after
the DATA or BDAT request deadline is decremented by the elapsed
time of that read operation, the DATA or BDAT request deadline is
incremented by N/smtpd_min_data_rate seconds. However, the deadline
will never be incremented beyond the time limit specified with
smtpd_timeout.

This feature is available in Postfix 3.7 and later.


(default: empty)

List of commands that the Postfix SMTP server replies to with “250
Ok”, without doing any syntax checks and without changing state.
This list overrides any commands built into the Postfix SMTP server.


(default: <>)

The lookup key to be used in SMTP access(5) tables instead of the
null sender address.


(default: yes)

Attempt to look up the remote SMTP client hostname, and verify that
the name matches the client IP address. A client name is set to
“unknown” when it cannot be looked up or verified, or when name
lookup is disabled. Turning off name lookup reduces delays due to
DNS lookup and increases the maximal inbound delivery rate.

This feature is available in Postfix 2.3 and later.


(default: normal: no, overload: yes)

Change the behavior of the smtpd_timeout and smtpd_starttls_timeout
time limits, from a
time limit per read or write system call, to a time limit to send
or receive a complete record (an SMTP command line, SMTP response
line, SMTP message content line, or TLS protocol message). This
limits the impact from hostile peers that trickle data one byte at
a time.

Note: when per-record deadlines are enabled, a short timeout
may cause problems with TLS over very slow network connections.
The reasons are that a TLS protocol message can be up to 16 kbytes
long (with TLSv1), and that an entire TLS protocol message must be
sent or received within the per-record deadline.

This feature is available in Postfix 2.9-3.6. With older
Postfix releases, the behavior is as if this parameter is set to
“no”. Postfix 3.7 and later use smtpd_per_request_deadline.


(default: normal: no, overload: yes)

Change the behavior of the smtpd_timeout and smtpd_starttls_timeout
time limits, from a time limit per plaintext or TLS read or write
call, to a combined time limit for receiving a complete SMTP request
and for sending a complete SMTP response. The deadline limits only
the time spent waiting for plaintext or TLS read or write calls,
not time spent elsewhere. The per-request deadline limits the impact
from hostile peers that trickle data one byte at a time.

See smtpd_min_data_rate for how the per-request deadline is
managed during the DATA and BDAT phase.

Note: when per-request deadlines are enabled, a short time limit
may cause problems with TLS over very slow network connections. The
reason is that a TLS protocol message can be up to 16 kbytes long
(with TLSv1), and that an entire TLS protocol message must be
transferred within the per-request deadline.

This feature is available in Postfix 3.7 and later. A weaker
feature, called smtpd_per_record_deadline, is available with Postfix
2.9-3.6. With older Postfix releases, the behavior is as if this
parameter is set to “no”.

This feature is available in Postfix 3.7 and later.


(default: 451 4.3.5 Server configuration problem)

The default action when an SMTPD policy service request fails.
Specify “DUNNO” to behave as if the failed SMTPD policy service
request was not sent, and to continue processing other access
restrictions, if any.

Limitations:

This feature is available in Postfix 3.0 and later.


(default: 300s)

The time after which an idle SMTPD policy service connection is
closed.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: 1000s)

The time after which an active SMTPD policy service connection is
closed.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: empty)

Optional information that the Postfix SMTP server specifies in
the “policy_context” attribute of a policy service request (originally,
to share the same service endpoint among multiple check_policy_service
clients).

This feature is available in Postfix 3.1 and later.


(default: 0)

The maximal number of requests per SMTPD policy service connection,
or zero (no limit). Once a connection reaches this limit, the
connection is closed and the next request will be sent over a new
connection. This is a workaround to avoid error-recovery delays
with policy servers that cannot maintain a persistent connection.

This feature is available in Postfix 3.0 and later.


(default: 1s)

The delay between attempts to resend a failed SMTPD policy
service request. Specify a value greater than zero.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 3.0 and later.


(default: 100s)

The time limit for connecting to, writing to, or receiving from a
delegated SMTPD policy server.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: 2)

The maximal number of attempts to send an SMTPD policy service
request before giving up. Specify a value greater than zero.

This feature is available in Postfix 3.0 and later.


(default: $myhostname)

How the Postfix SMTP server announces itself to the proxy filter.
By default, the Postfix hostname is used.

This feature is available in Postfix 2.1 and later.


(default: empty)

The hostname and TCP port of the mail filtering proxy server.
The proxy receives all mail from the Postfix SMTP server, and is
supposed to give the result to another Postfix SMTP server process.

Specify “host:port” or “inet:host:port” for a TCP endpoint, or
“unix:pathname” for a UNIX-domain endpoint. The host can be specified
as an IP address or as a symbolic name; no MX lookups are done.
When no “host” or “host:” is specified, the local machine is
assumed. Pathname interpretation is relative to the Postfix queue
directory.

This feature is available in Postfix 2.1 and later.

The “inet:” and “unix:” prefixes are available in Postfix 2.3
and later.


(default: empty)

List of options that control how the Postfix SMTP server
communicates with a before-queue content filter. Specify zero or
more of the following, separated by comma or whitespace.

speed_adjust

Do not connect to a before-queue content filter until an entire
message has been received. This reduces the number of simultaneous
before-queue content filter processes.

NOTE 1: A filter must not selectively reject recipients
of a multi-recipient message. Rejecting all recipients is OK, as
is accepting all recipients.

NOTE 2: This feature increases the minimum amount of free queue
space by $message_size_limit. The extra space is needed to save the
message to a temporary file.

This feature is available in Postfix 2.7 and later.


(default: 100s)

The time limit for connecting to a proxy filter and for sending or
receiving information. When a connection fails the client gets a
generic error message while more detailed information is logged to
the maillog file.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.


(default: 1000)

The maximal number of recipients that the Postfix SMTP server
accepts per message delivery request.


(default: 1000)

The number of recipients that a remote SMTP client can send in
excess of the limit specified with $smtpd_recipient_limit, before
the Postfix SMTP server increments the per-session error count
for each excess recipient.


(default: see “postconf -d” output)

Optional restrictions that the Postfix SMTP server applies in the
context of a client RCPT TO command, after smtpd_relay_restrictions.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

With Postfix versions before 2.10, the rules for relay permission
and spam blocking were combined under smtpd_recipient_restrictions,
resulting in error-prone configuration. As of Postfix 2.10, relay
permission rules are preferably implemented with smtpd_relay_restrictions,
so that a permissive spam blocking policy under
smtpd_recipient_restrictions will no longer result in a permissive
mail relay policy.

For backwards compatibility, sites that migrate from Postfix
versions before 2.10 can set smtpd_relay_restrictions to the empty
value, and use smtpd_recipient_restrictions exactly as before.

IMPORTANT: Either the smtpd_relay_restrictions or the
smtpd_recipient_restrictions parameter must specify
at least one of the following restrictions. Otherwise Postfix will
refuse to receive mail:

reject, reject_unauth_destination

defer, defer_if_permit, defer_unauth_destination

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.

The following restrictions are specific to the recipient address
that is received with the RCPT TO command.

type:table
Search the specified access(5) database for the resolved RCPT
TO address, domain, parent domains, or localpart@, and execute the
corresponding action.
type:table
Search the specified access(5) database for the IP addresses for
the RCPT TO domain, and execute the corresponding action. Note:
a result of “OK” is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from denylists. This
feature is available in Postfix 3.0 and later.
type:table
Search the specified access(5) database for the MX hosts for
the RCPT TO domain, and execute the corresponding action. If no
MX record is found, look up A or AAAA records, just like the Postfix
SMTP client would. Note:
a result of “OK” is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from denylists. This
feature is available in Postfix 2.1 and later.
type:table
Search the specified access(5) database for the DNS servers
for the RCPT TO domain, and execute the corresponding action.
Note: a result of “OK” is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from denylists. This
feature is available in Postfix 2.1 and later.
Permit the request when one of the following is true:

Permit the request when the local mail system is a backup MX for
the RCPT TO domain, or when the domain is an authorized destination
(see permit_auth_destination for definition).

Reject the request when the RCPT TO address specifies a
domain that is not in
fully-qualified domain form, as required by the RFC.
The
non_fqdn_reject_code parameter specifies the response code for
rejected requests (default: 504).
Reject the request when the RCPT TO domain is listed with the
A record “d.d.d.d” under rbl_domain (Postfix version
2.1 and later only). Each “d” is a number, or a pattern
inside “[]” that contains one or more “;”-separated numbers or
number..number ranges (Postfix version 2.8 and later). If no
=d.d.d.d” is specified, reject
the request when the RCPT TO domain is listed with
any A record under rbl_domain.
The maps_rbl_reject_code
parameter specifies the response code for rejected requests (default:
554); the default_rbl_reply parameter specifies the default server
reply; and the rbl_reply_maps parameter specifies tables with server
replies indexed by rbl_domain. This feature is available
in Postfix version 2.0 and later.
Reject the request unless one of the following is true:

The relay_domains_reject_code parameter specifies the response
code for rejected requests (default: 554).

Reject the same requests as reject_unauth_destination, with a
non-permanent error code. This feature is available in Postfix
2.10 and later.
Reject the request when Postfix is not final destination for
the recipient domain, and the RCPT TO domain has 1) no DNS MX and
no DNS A
record or 2) a malformed MX record such as a record with
a zero-length MX hostname (Postfix version 2.3 and later).
The
reply is specified with the unknown_address_reject_code parameter
(default: 450), unknown_address_tempfail_action (default:
defer_if_permit), or 556 (nullmx, Postfix 3.0 and
later). See the respective parameter descriptions for details.
(with Postfix version 2.0: check_recipient_maps)
Reject the request when the RCPT TO address is not listed in
the list of valid recipients for its domain class. See the
smtpd_reject_unlisted_recipient parameter description for details.
This feature is available in Postfix 2.1 and later.
Reject the request when mail to the RCPT TO address is known
to bounce, or when the recipient address destination is not reachable.
Address verification information is managed by the verify(8) server;
see the ADDRESS_VERIFICATION_README file for details.
The
unverified_recipient_reject_code parameter specifies the numerical
response code when an address is known to bounce (default: 450,
change it to 550 when you are confident that it is safe to do so).

The unverified_recipient_defer_code parameter specifies the
numerical response code when an address probe failed due to a
temporary problem (default: 450).
The
unverified_recipient_tempfail_action parameter specifies the action
after address probe failure due to a temporary problem (default:
defer_if_permit).
This feature breaks for aliased addresses
with “enable_original_recipient = no” (Postfix ≤ 3.2).
This feature is available in Postfix 2.1 and later.

Other restrictions that are valid in this context:

Example:

# The Postfix before 2.10 default mail relay policy. Later Postfix
# versions implement this preferably with smtpd_relay_restrictions.
smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

(default: empty)

Optional information that is appended after each Postfix SMTP
server
4XX or 5XX response.

The following example uses “c” at the start of the template
(supported in Postfix 2.10 and later) to suppress the line break
between the reply text and the footer text. With earlier Postfix
versions, the footer text always begins on a new line, and the “c”
is output literally.

/etc/postfix/main.cf:
    smtpd_reject_footer = c. For assistance, call 800-555-0101.
     Please provide the following information in your problem report:
     time ($localtime), client ($client_address) and server
     ($server_name).

Server response:

    550-5.5.1 <user@example> Recipient address rejected: User
    unknown. For assistance, call 800-555-0101. Please provide the
    following information in your problem report: time (Jan 4 15:42:00),
    client (192.168.1.248) and server (mail1.example.com).

Note: the above text is meant to make it easier to find the
Postfix logfile records for a failed SMTP session. The text itself
is not logged to the Postfix SMTP server’s maillog file.

Be sure to keep the text as short as possible. Long text may
be truncated before it is logged to the remote SMTP client’s maillog
file, or before it is returned to the sender in a delivery status
notification.

The template text is not subject to Postfix configuration
parameter $name expansion. Instead, this feature supports a limited
number of $name attributes in the footer text. These attributes are
replaced with their current value for the SMTP session.

Note: specify $$name in footer text that is looked up from
regexp: or pcre:-based smtpd_reject_footer_maps, otherwise the
Postfix server will not use the footer text and will log a warning
instead.

client_address
The Client IP address that
is logged in the maillog file.
client_port
The client TCP port that is
logged in the maillog file.
localtime
The server local time (Mmm dd
hh:mm:ss) that is logged in the maillog file.
server_name
The server’s myhostname value.
This attribute is made available for sites with multiple MTAs
(perhaps behind a load-balancer), where the server name can help
the server support team to quickly find the right log files.

Notes:

This feature supports the two-character sequence n as a request
for a line break in the footer text. Postfix automatically inserts
after each line break the three-digit SMTP reply code (and optional
enhanced status code) from the original Postfix reject message.

To work around mail software that mis-handles multi-line replies,
specify the two-character sequence c at the start of the template.
This suppresses the line break between the reply text and the footer
text (Postfix 2.10 and later).

This feature is available in Postfix 2.8 and later.


(default: empty)

Lookup tables, indexed by the complete Postfix SMTP server 4xx or
5xx response, with reject footer templates. See smtpd_reject_footer
for details.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

This feature is available in Postfix 3.4 and later.


(default: yes)

Request that the Postfix SMTP server rejects mail for unknown
recipient addresses, even when no explicit reject_unlisted_recipient
access restriction is specified. This prevents the Postfix queue
from filling up with undeliverable MAILER-DAEMON messages.

An address is considered “unknown” when 1) it does not match a
virtual(5) alias or canonical(5) mapping, and 2) the address is not
valid for its address class. For a definition of class-based address
validation, see
ADDRESS_CLASS_README
.

This feature is available in Postfix 2.1 and later.


(default: no)

Request that the Postfix SMTP server rejects mail from unknown
sender addresses, even when no explicit reject_unlisted_sender
access restriction is specified. This can slow down an explosion
of forged mail from worms or viruses.

An address is considered “unknown” when 1) it does not match a
virtual(5) alias or canonical(5) mapping, and 2) the address is not
valid for its address class. For a definition of class-based address
validation, see
ADDRESS_CLASS_README
.

This feature is available in Postfix 2.1 and later.


(default: see “postconf -d” output)

Evaluate smtpd_relay_restrictions before smtpd_recipient_restrictions.
Historically, smtpd_relay_restrictions was evaluated after
smtpd_recipient_restrictions, contradicting documented behavior.

Background: the smtpd_relay_restrictions feature is primarily
designed to enforce a mail relaying policy, while
smtpd_recipient_restrictions is primarily designed to enforce spam
blocking policy. Both are evaluated while replying to the RCPT TO
command, and both support the same features.

This feature is available in Postfix 3.6 and later.


(default: permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination)

Access restrictions for mail relay control that the Postfix
SMTP server applies in the context of the RCPT TO command, before
smtpd_recipient_restrictions.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

With Postfix versions before 2.10, the rules for relay permission
and spam blocking were combined under smtpd_recipient_restrictions,
resulting in error-prone configuration. As of Postfix 2.10, relay
permission rules are preferably implemented with smtpd_relay_restrictions,
so that a permissive spam blocking policy under
smtpd_recipient_restrictions will no longer result in a permissive
mail relay policy.

For backwards compatibility, sites that migrate from Postfix
versions before 2.10 can set smtpd_relay_restrictions to the empty
value, and use smtpd_recipient_restrictions exactly as before.

By default, the Postfix SMTP server accepts:

IMPORTANT: Either the smtpd_relay_restrictions or the
smtpd_recipient_restrictions parameter must specify
at least one of the following restrictions. Otherwise Postfix will
refuse to receive mail:

reject, reject_unauth_destination

defer, defer_if_permit, defer_unauth_destination

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
The same restrictions are available as documented under
smtpd_recipient_restrictions.

This feature is available in Postix 2.10 and later.


(default: empty)

User-defined aliases for groups of access restrictions. The aliases
can be specified in smtpd_recipient_restrictions etc., and on the
right-hand side of a Postfix access(5) table.

One major application is for implementing per-recipient UCE control.
See the RESTRICTION_CLASS_README document for other examples.


(default: smtpd)

The application name that the Postfix SMTP server uses for SASL
server initialization. This
controls the name of the SASL configuration file. The default value
is smtpd, corresponding to a SASL configuration file named
smtpd.conf.

This feature is available in Postfix 2.1 and 2.2. With Postfix 2.3
it was renamed to smtpd_sasl_path.


(default: no)

Enable SASL authentication in the Postfix SMTP server. By default,
the Postfix SMTP server does not use authentication.

If a remote SMTP client is authenticated, the permit_sasl_authenticated
access restriction can be used to permit relay access, like this:

# With Postfix 2.10 and later, the mail relay policy is
# preferably specified under smtpd_relay_restrictions.
smtpd_relay_restrictions =
    permit_mynetworks, permit_sasl_authenticated, ...
# With Postfix before 2.10, the relay policy can be
# specified only under smtpd_recipient_restrictions.
smtpd_recipient_restrictions =
    permit_mynetworks, permit_sasl_authenticated, ...

To reject all SMTP connections from unauthenticated clients,
specify “smtpd_delay_reject = yes” (which is the default) and use:

smtpd_client_restrictions = permit_sasl_authenticated, reject

See the SASL_README file for SASL configuration and operation details.


(default: no)

Report the SASL authenticated user name in the smtpd(8) Received
message header.

This feature is available in Postfix 2.3 and later.


(default: empty)

What remote SMTP clients the Postfix SMTP server will not offer
AUTH support to.

Some clients (Netscape 4 at least) have a bug that causes them to
require a login and password whenever AUTH is offered, whether it’s
necessary or not. To work around this, specify, for example,
$mynetworks to prevent Postfix from offering AUTH to local clients.

Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify “/file/name” or
type:table” patterns. A “/file/name” pattern is replaced by its
contents; a “type:table” lookup table is matched when a table entry
matches a lookup string (the lookup result is ignored). Continue
long lines by starting the next line with whitespace. Specify
“!pattern” to exclude an address or network block from the list.
The form “!/file/name” is supported only in Postfix version 2.4 and
later.

Note: IP version 6 address information must be specified inside
[] in the smtpd_sasl_exceptions_networks value, and in
files specified with “/file/name”. IP version 6 addresses contain
the “:” character, and would otherwise be confused with a “type:table
pattern.

Example:

smtpd_sasl_exceptions_networks = $mynetworks

This feature is available in Postfix 2.1 and later.


(default: empty)

The name of the Postfix SMTP server’s local SASL authentication
realm.

By default, the local authentication realm name is the null string.

Examples:

smtpd_sasl_local_domain = $mydomainsmtpd_sasl_local_domain = $myhostname

(default: !external, static:rest)

If non-empty, a filter for the SASL mechanism names that the
Postfix SMTP server will announce in the EHLO response. By default,
the Postfix SMTP server will not announce the EXTERNAL mechanism,
because Postfix support for that is not implemented.

Specify mechanism names, “/file/name” patterns, or “type:table
lookup tables, separated by comma or whitespace. The right-hand
side result from “type:table” lookups is ignored. Specify “!pattern”
to exclude a mechanism name from the list.

Examples:

smtpd_sasl_mechanism_filter = !external, !gssapi, static:rest
smtpd_sasl_mechanism_filter = login, plain
smtpd_sasl_mechanism_filter = /etc/postfix/smtpd_mechs

This feature is available in Postfix 3.6 and later.


(default: smtpd)

Implementation-specific information that the Postfix SMTP server
passes through to
the SASL plug-in implementation that is selected with
smtpd_sasl_type. Typically this specifies the name of a
configuration file or rendezvous point.

This feature is available in Postfix 2.3 and later. In earlier
releases it was called smtpd_sasl_application_name.


(default: 12288)

The maximum length of a SASL client’s response to a server challenge.
When the client’s “initial response” is longer than the normal limit for
SMTP commands, the client must omit its initial response, and wait for an
empty server challenge; it can then send what would have been its “initial
response” as a response to the empty server challenge. RFC4954 requires the
server to accept client responses up to at least 12288 octets of
base64-encoded text. The default value is therefore also the minimum value
accepted for this parameter.

This feature is available in Postfix 3.4 and later. Prior versions use
line_length_limit“, which may need to be raised to accommodate larger client
responses, as may be needed with GSSAPI authentication of Windows AD users
who are members of many groups.


(default: noanonymous)

Postfix SMTP server SASL security options; as of Postfix 2.3
the list of available
features depends on the SASL server implementation that is selected
with smtpd_sasl_type.

The following security features are defined for the cyrus
server SASL implementation:

Restrict what authentication mechanisms the Postfix SMTP server
will offer to the client. The list of available authentication
mechanisms is system dependent.

Specify zero or more of the following:

noplaintext
Disallow methods that use plaintext passwords.
noactive
Disallow methods subject to active (non-dictionary) attack.
nodictionary
Disallow methods subject to passive (dictionary) attack.
noanonymous
Disallow methods that allow anonymous authentication.
forward_secrecy
Only allow methods that support forward secrecy (Dovecot only).
mutual_auth
Only allow methods that provide mutual authentication (not available
with Cyrus SASL version 1).

By default, the Postfix SMTP server accepts plaintext passwords but
not anonymous logins.

Warning: it appears that clients try authentication methods in the
order as advertised by the server (e.g., PLAIN ANONYMOUS CRAM-MD5)
which means that if you disable plaintext passwords, clients will
log in anonymously, even when they should be able to use CRAM-MD5.
So, if you disable plaintext logins, disable anonymous logins too.
Postfix treats anonymous login as no authentication.

Example:

smtpd_sasl_security_options = noanonymous, noplaintext

(default: smtp)

The service name that is passed to the SASL plug-in that is
selected with smtpd_sasl_type and smtpd_sasl_path.

This feature is available in Postfix 2.11 and later. Prior
versions behave as if “smtp” is specified.


(default: $smtpd_sasl_security_options)

The SASL authentication security options that the Postfix SMTP
server uses for TLS encrypted SMTP sessions.

This feature is available in Postfix 2.2 and later.


(default: cyrus)

The SASL plug-in type that the Postfix SMTP server should use
for authentication. The available types are listed with the
postconf -a” command.

This feature is available in Postfix 2.3 and later.


(default: empty)

Optional lookup table with the SASL login names that own the sender
(MAIL FROM) addresses.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found. With lookups from
indexed files such as DB or DBM, or from networked tables such as
NIS, LDAP or SQL, the following search operations are done with a
sender address of user@domain:

1) user@domain
This table lookup is always done and has the highest precedence.
2) user
This table lookup is done only when the domain part of the
sender address matches $myorigin, $mydestination, $inet_interfaces
or $proxy_interfaces.
3) @domain
This table lookup is done last and has the lowest precedence.

In all cases the result of table lookup must be either “not found”
or a list of SASL login names separated by comma and/or whitespace.


(default: empty)

Optional restrictions that the Postfix SMTP server applies in the
context of a client MAIL FROM command.
See SMTPD_ACCESS_README, section “Delayed evaluation of SMTP access
restriction lists” for a discussion of evaluation context and time.

The default is to permit everything.

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.

The following restrictions are specific to the sender address
received with the MAIL FROM command.

type:table
Search the specified access(5) database for the MAIL FROM
address, domain, parent domains, or localpart@, and execute the
corresponding action.
type:table
Search the specified access(5) database for the IP addresses for
the MAIL FROM domain, and execute the corresponding action. Note:
a result of “OK” is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from denylists. This
feature is available in Postfix 3.0 and later.
type:table
Search the specified access(5) database for the MX hosts for
the MAIL FROM domain, and execute the corresponding action. If no
MX record is found, look up A or AAAA records, just like the Postfix
SMTP client would. Note:
a result of “OK” is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from denylists. This
feature is available in Postfix 2.1 and later.
type:table
Search the specified access(5) database for the DNS servers
for the MAIL FROM domain, and execute the corresponding action.
Note: a result of “OK” is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from denylists. This
feature is available in Postfix 2.1 and later.
Reject the request when the client is authenticated with SASL,
but either the MAIL FROM address is not listed in $smtpd_sender_login_maps,
or the SASL login name is not an owner for that address.

This prevents an authenticated client from using a MAIL FROM address
that they do not explicitly own.

This feature is available in Postfix version 2.1 and later.
When the client is authenticated with SASL, reject the request
when the MAIL FROM address is listed in $smtpd_sender_login_maps,
but the SASL login name is not an owner for that address.

When the client is not authenticated with SASL, reject the request
when SASL is enabled, and the MAIL FROM address is listed in
$smtpd_sender_login_maps.

This protects any MAIL FROM address that is listed in
$smtpd_sender_login_maps, while still allowing a client to use any
unlisted MAIL FROM address.

This feature is available in Postfix version 2.11 and later.
Reject the request when the MAIL FROM address specifies a
domain that is not in
fully-qualified domain form as required by the RFC.
The
non_fqdn_reject_code parameter specifies the response code for
rejected requests (default: 504).
Reject the request when the MAIL FROM domain is listed with
the A record “d.d.d.d” under rbl_domain (Postfix
version 2.1 and later only). Each “d” is a number, or a
pattern inside “[]” that contains one or more “;”-separated numbers
or number..number ranges (Postfix version 2.8 and later). If no
=d.d.d.d” is specified,
reject the request when the MAIL FROM domain is
listed with any A record under rbl_domain.
The
maps_rbl_reject_code parameter specifies the response code for
rejected requests (default: 554); the default_rbl_reply parameter
specifies the default server reply; and the rbl_reply_maps parameter
specifies tables with server replies indexed by rbl_domain.
This feature is available in Postfix 2.0 and later.
As of Postfix 2.1, this is an alias for
reject_authenticated_sender_login_mismatch,
reject_unauthenticated_sender_login_mismatch“.
Reject the request when SASL is enabled, the MAIL FROM address
is listed in $smtpd_sender_login_maps, but the client is not
authenticated with SASL.

With SASL enabled, this prevents an unauthenticated client from
using any MAIL FROM address that is listed in $smtpd_sender_login_maps.

This feature is available in Postfix version 2.1 and later.
Reject the request when Postfix is not the final destination for
the sender address, and the MAIL FROM domain has 1) no DNS MX and
no DNS A
record, or 2) a malformed MX record such as a record with
a zero-length MX hostname (Postfix version 2.3 and later).
The
reply is specified with the unknown_address_reject_code parameter
(default: 450), unknown_address_tempfail_action (default:
defer_if_permit), or 550 (nullmx, Postfix 3.0 and
later). See the respective parameter descriptions for details.
Reject the request when the MAIL FROM address is not listed in
the list of valid recipients for its domain class. See the
smtpd_reject_unlisted_sender parameter description for details.
This feature is available in Postfix 2.1 and later.
Reject the request when mail to the MAIL FROM address is known to
bounce, or when the sender address destination is not reachable.
Address verification information is managed by the verify(8) server;
see the ADDRESS_VERIFICATION_README file for details.
The
unverified_sender_reject_code parameter specifies the numerical
response code when an address is known to bounce (default: 450,
change into 550 when you are confident that it is safe to do so).

The unverified_sender_defer_code specifies the numerical response
code when an address probe failed due to a temporary problem
(default: 450).
The unverified_sender_tempfail_action parameter
specifies the action after address probe failure due to a temporary
problem (default: defer_if_permit).
This feature breaks for
aliased addresses with “enable_original_recipient = no” (Postfix
≤ 3.2).
This feature is available in Postfix 2.1 and later.

Other restrictions that are valid in this context:

Examples:

smtpd_sender_restrictions = reject_unknown_sender_domainsmtpd_sender_restrictions = reject_unknown_sender_domain,
    check_sender_accesshash:/etc/postfix/access

(default: smtpd)

The internal service that postscreen(8) hands off allowed
connections to. In a future version there may be different
classes of SMTP service.

This feature is available in Postfix 2.8.


(default: 10)

The number of errors a remote SMTP client is allowed to make without
delivering mail before the Postfix SMTP server slows down all its
responses.


(default: see “postconf -d” output)

The time limit for Postfix SMTP server write and read operations
during TLS startup and shutdown handshake procedures. The current
default value is stress-dependent. Before Postfix version 2.8, it
was fixed at 300s.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.2 and later.


(default: normal: 300s, overload: 10s)

When the Postfix SMTP server wants to send an SMTP server
response, how long the Postfix SMTP server will wait for an underlying
network write operation to complete; and when the Postfix SMTP
server Postfix wants to receive an SMTP client request, how long
the Postfix SMTP server will wait for an underlying network read
operation to complete. See the smtpd_per_request_deadline for how
this time limit may be enforced (with Postfix 2.9-3.6 see
smtpd_per_record_deadline).

Normally the default limit
is 300s, but it changes under overload to just 10s. With Postfix
2.5 and earlier, the SMTP server always uses a time limit of 300s
by default.

Note: if you set SMTP time limits to very large values you may have
to update the global ipc_timeout parameter.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

A file containing (PEM format) CA certificates of root CAs trusted
to sign either remote SMTP client certificates or intermediate CA
certificates. These are loaded into memory before the smtpd(8) server
enters the chroot jail. If the number of trusted roots is large, consider
using smtpd_tls_CApath instead, but note that the latter directory must
be present in the chroot jail if the smtpd(8) server is chrooted. This
file may also be used to augment the server certificate trust chain,
but it is best to include all the required certificates directly in the
server certificate file.

Specify “smtpd_tls_CAfile = /path/to/system_CA_file” to use ONLY
the system-supplied default Certification Authority certificates.

Specify “tls_append_default_CA = no” to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates.

By default (see smtpd_tls_ask_ccert), client certificates are not
requested, and smtpd_tls_CAfile should remain empty. If you do make use
of client certificates, the distinguished names (DNs) of the Certification
Authorities listed in smtpd_tls_CAfile are sent to the remote SMTP client
in the client certificate request message. MUAs with multiple client
certificates may use the list of preferred Certification Authorities
to select the correct client certificate. You may want to put your
“preferred” CA or CAs in this file, and install other trusted CAs in
$smtpd_tls_CApath.

Example:

smtpd_tls_CAfile = /etc/postfix/CAcert.pem

This feature is available in Postfix 2.2 and later.


(default: empty)

A directory containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or intermediate CA
certificates. Do not forget to create the necessary “hash” links with,
for example, “$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs”. To use
smtpd_tls_CApath in chroot mode, this directory (or a copy) must be
inside the chroot jail.

Specify “smtpd_tls_CApath = /path/to/system_CA_directory” to
use ONLY the system-supplied default Certification Authority certificates.

Specify “tls_append_default_CA = no” to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates.

By default (see smtpd_tls_ask_ccert), client certificates are
not requested, and smtpd_tls_CApath should remain empty. In contrast
to smtpd_tls_CAfile, DNs of Certification Authorities installed
in $smtpd_tls_CApath are not included in the client certificate
request message. MUAs with multiple client certificates may use the
list of preferred Certification Authorities to select the correct
client certificate. You may want to put your “preferred” CA or
CAs in $smtpd_tls_CAfile, and install the remaining trusted CAs in
$smtpd_tls_CApath.

Example:

smtpd_tls_CApath = /etc/postfix/certs

This feature is available in Postfix 2.2 and later.


(default: yes)

Force the Postfix SMTP server to issue a TLS session id, even
when TLS session caching is turned off (smtpd_tls_session_cache_database
is empty). This behavior is compatible with Postfix < 2.3.

With Postfix 2.3 and later the Postfix SMTP server can disable
session id generation when TLS session caching is turned off. This
keeps remote SMTP clients from caching sessions that almost certainly cannot
be re-used.

By default, the Postfix SMTP server always generates TLS session
ids. This works around a known defect in mail client applications
such as MS Outlook, and may also prevent interoperability issues
with other MTAs.

Example:

smtpd_tls_always_issue_session_ids = no

This feature is available in Postfix 2.3 and later.


(default: no)

Ask a remote SMTP client for a client certificate. This
information is needed for certificate based mail relaying with,
for example, the permit_tls_clientcerts feature.

Some clients such as Netscape will either complain if no
certificate is available (for the list of CAs in $smtpd_tls_CAfile)
or will offer multiple client certificates to choose from. This
may be annoying, so this option is “off” by default.

This feature is available in Postfix 2.2 and later.


(default: no)

When TLS encryption is optional in the Postfix SMTP server, do
not announce or accept SASL authentication over unencrypted
connections.

This feature is available in Postfix 2.2 and later.


(default: 9)

The verification depth for remote SMTP client certificates. A
depth of 1 is sufficient if the issuing CA is listed in a local CA
file.

The default verification depth is 9 (the OpenSSL default) for
compatibility with earlier Postfix behavior. Prior to Postfix 2.5,
the default value was 5, but the limit was not actually enforced. If
you have set this to a lower non-default value, certificates with longer
trust chains may now fail to verify. Certificate chains with 1 or 2
CAs are common, deeper chains are more rare and any number between 5
and 9 should suffice in practice. You can choose a lower number if,
for example, you trust certificates directly signed by an issuing CA
but not any CAs it delegates to.

This feature is available in Postfix 2.2 and later.


(default: empty)

File with the Postfix SMTP server RSA certificate in PEM format.
This file may also contain the Postfix SMTP server private RSA key.
With Postfix ≥ 3.4 the preferred way to configure server keys and
certificates is via the “smtpd_tls_chain_files” parameter.

Public Internet MX hosts without certificates signed by a “reputable”
CA must generate, and be prepared to present to most clients, a
self-signed or private-CA signed certificate. The client will not be
able to authenticate the server, but unless it is running Postfix 2.3 or
similar software, it will still insist on a server certificate.

For servers that are not public Internet MX hosts, Postfix
supports configurations with no certificates. This entails the use of
just the anonymous TLS ciphers, which are not supported by typical SMTP
clients. Since some clients may not fall back to plain text after a TLS
handshake failure, a certificate-less Postfix SMTP server will be unable
to receive email from some TLS-enabled clients. To avoid accidental
configurations with no certificates, Postfix enables certificate-less
operation only when the administrator explicitly sets
smtpd_tls_cert_file = none”. This ensures that new Postfix SMTP server
configurations will not accidentally enable TLS without certificates.

Note that server certificates are not optional in TLS 1.3. To run
without certificates you’d have to disable the TLS 1.3 protocol by
including ‘!TLSv1.3’ in “smtpd_tls_protocols” and perhaps also
smtpd_tls_mandatory_protocols“. It is simpler instead to just
configure a certificate chain. Certificate-less operation is not
recommended.

Both RSA and DSA certificates are supported. When both types
are present, the cipher used determines which certificate will be
presented to the client. For Netscape and OpenSSL clients without
special cipher choices the RSA certificate is preferred.

To enable a remote SMTP client to verify the Postfix SMTP server
certificate, the issuing CA certificates must be made available to the
client. You should include the required certificates in the server
certificate file, the server certificate first, then the issuing
CA(s) (bottom-up order).

Example: the certificate for “server.example.com” was issued by
“intermediate CA” which itself has a certificate of “root CA”.
Create the server.pem file with “cat server_cert.pem intermediate_CA.pem
root_CA.pem > server.pem”.

If you also want to verify client certificates issued by these
CAs, you can add the CA certificates to the smtpd_tls_CAfile, in which
case it is not necessary to have them in the smtpd_tls_cert_file,
smtpd_tls_dcert_file (obsolete) or smtpd_tls_eccert_file.

A certificate supplied here must be usable as an SSL server certificate
and hence pass the “openssl verify -purpose sslserver …” test.

Example:

smtpd_tls_cert_file = /etc/postfix/server.pem

This feature is available in Postfix 2.2 and later.


(default: empty)

List of one or more PEM files, each holding one or more private keys
directly followed by a corresponding certificate chain. The file names
are separated by commas and/or whitespace. This parameter obsoletes the
legacy algorithm-specific key and certificate file settings. When this
parameter is non-empty, the legacy parameters are ignored, and a warning
is logged if any are also non-empty.

With the proliferation of multiple private key algorithms—which,
as of OpenSSL 1.1.1, include DSA (obsolete), RSA, ECDSA, Ed25519
and Ed448—it is increasingly impractical to use separate
parameters to configure the key and certificate chain for each
algorithm. Therefore, Postfix now supports storing multiple keys and
corresponding certificate chains in a single file or in a set of files.

Each key must appear immediately before the corresponding
certificate, optionally followed by additional issuer certificates that
complete the certificate chain for that key. When multiple files are
specified, they are equivalent to a single file that is concatenated
from those files in the given order. Thus, while a key must always
precede its certificate and issuer chain, it can be in a separate file,
so long as that file is listed immediately before the file that holds
the corresponding certificate chain. Once all the files are
concatenated, the sequence of PEM objects must be: key1, cert1,
[chain1], key2, cert2, [chain2], …, keyN, certN, [chainN].

Storing the private key in the same file as the corresponding
certificate is more reliable. With the key and certificate in separate
files, there is a chance that during key rollover a Postfix process
might load a private key and certificate from separate files that don’t
match. Various operational errors may even result in a persistent
broken configuration in which the certificate does not match the private
key.

The file or files must contain at most one key of each type. If,
for example, two or more RSA keys and corresponding chains are listed,
depending on the version of OpenSSL either only the last one will be
used or a configuration error may be detected. Note that while
“Ed25519” and “Ed448” are considered separate algorithms, the various
ECDSA curves (typically one of prime256v1, secp384r1 or secp521r1) are
considered as different parameters of a single “ECDSA” algorithm, so it
is not presently possible to configure keys for more than one ECDSA
curve.

RSA is still the most widely supported algorithm. Presently (late
2022), ECDSA support is common, but not yet universal, and Ed25519 and
Ed448 support is mostly absent. Therefore, an RSA key should generally
be configured, along with any additional keys for the other algorithms
when desired.

Example (separate files for each key and corresponding certificate chain):

/etc/postfix/main.cf:
    smtpd_tls_chain_files =
        ${config_directory}/ed25519.pem,
        ${config_directory}/ed448.pem,
        ${config_directory}/rsa.pem

/etc/postfix/ed25519.pem:
    -----BEGIN PRIVATE KEY-----
    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH Efbz3
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBKzCB3qADAgECAhQaw rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
    ...
    nC0egv51YPDWxEHom4QA
    -----END CERTIFICATE-----

/etc/postfix/ed448.pem:
    -----BEGIN PRIVATE KEY-----
    MEcCAQAwBQYDK2VxBDsEOQf m0P G0qi NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
    ...
    pQcWsx 4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ eeYOxyThMA
    -----END CERTIFICATE-----

/etc/postfix/rsa.pem:
    -----BEGIN PRIVATE KEY-----
    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
    ...
    ahQkZ3 krcaJvDSMgvu0tDc=
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIC DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
    ...
    Rirz15HGVNTK8wzFd nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
    -----END CERTIFICATE-----

Example (all keys and certificates in a single file):

/etc/postfix/main.cf:
    smtpd_tls_chain_files = ${config_directory}/chains.pem

/etc/postfix/chains.pem:
    -----BEGIN PRIVATE KEY-----
    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH Efbz3
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBKzCB3qADAgECAhQaw rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
    ...
    nC0egv51YPDWxEHom4QA
    -----END CERTIFICATE-----
    -----BEGIN PRIVATE KEY-----
    MEcCAQAwBQYDK2VxBDsEOQf m0P G0qi NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
    ...
    pQcWsx 4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ eeYOxyThMA
    -----END CERTIFICATE-----
    -----BEGIN PRIVATE KEY-----
    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
    ...
    ahQkZ3 krcaJvDSMgvu0tDc=
    -----END PRIVATE KEY-----
    -----BEGIN CERTIFICATE-----
    MIIC DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
    ...
    Rirz15HGVNTK8wzFd nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
    -----END CERTIFICATE-----

This feature is available in Postfix 3.4 and later.


(default: empty)

Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS
cipher list. It is easy to create interoperability problems by choosing
a non-default cipher list. Do not use a non-default TLS cipherlist for
MX hosts on the public Internet. Clients that begin the TLS handshake,
but are unable to agree on a common cipher, may not be able to send any
email to the SMTP server. Using a restricted cipher list may be more
appropriate for a dedicated MSA or an internal mailhub, where one can
exert some control over the TLS software and settings of the connecting
clients.

Note: do not use “” quotes around the parameter value.

This feature is available with Postfix version 2.2. It is not used with
Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead.


(default: medium)

The minimum TLS cipher grade that the Postfix SMTP server
will use with opportunistic TLS encryption. Cipher types listed in
smtpd_tls_exclude_ciphers are excluded from the base definition of
the selected cipher grade. The default value is “medium” for Postfix
releases after the middle of 2022, “export” for older releases.

When TLS is mandatory the cipher grade is chosen via the
smtpd_tls_mandatory_ciphers configuration parameter, see there for syntax
details.

This feature is available in Postfix 2.6 and later. With earlier Postfix
releases only the smtpd_tls_mandatory_ciphers parameter is implemented,
and opportunistic TLS always uses “export” or better (i.e. all) ciphers.


(default: empty)

File with the Postfix SMTP server DSA certificate in PEM format.
This file may also contain the Postfix SMTP server private DSA key.
The DSA algorithm is obsolete and should not be used.

See the discussion under smtpd_tls_cert_file for more details.

Example:

smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

This feature is available in Postfix 2.2 and later.


(default: empty)

File with DH parameters that the Postfix SMTP server should
use with non-export EDH ciphers.

With Postfix ≥ 3.7, built with OpenSSL version is 3.0.0 or later, if the
parameter value is either empty or “auto“, then the DH parameter
selection is delegated to the OpenSSL library, which selects appropriate
parameters based on the TLS handshake. This choice is likely to be the most
interoperable with SMTP clients using various TLS libraries, and custom local
parameters are no longer recommended when using Postfix ≥ 3.7 built against
OpenSSL 3.0.0.

The best-practice choice of parameters uses a 2048-bit prime. This is fine,
despite the historical “1024” in the parameter name. Do not be tempted to use
much larger values, performance degrades quickly, and you may also cease to
interoperate with some mainstream SMTP clients. As of Postfix 3.1, the
compiled-in default prime is 2048-bits, and it is not strictly necessary,
though perhaps somewhat beneficial to generate custom DH parameters.

Instead of using the exact same parameter sets as distributed
with other TLS packages, it is more secure to generate your own
set of parameters with something like the following commands:

openssl dhparam -out /etc/postfix/dh2048.pem 2048
openssl dhparam -out /etc/postfix/dh1024.pem 1024
# As of Postfix 3.6, export-grade 512-bit DH parameters are no longer
# supported or needed.
openssl dhparam -out /etc/postfix/dh512.pem 512

It is safe to share the same DH parameters between multiple
Postfix instances. If you prefer, you can generate separate
parameters for each instance.

If you want to take maximal advantage of ciphers that offer forward secrecy see
the Getting
started
section of FORWARD_SECRECY_README. The
full document conveniently presents all information about Postfix
“perfect” forward secrecy support in one place: what forward secrecy
is, how to tweak settings, and what you can expect to see when
Postfix uses ciphers with forward secrecy.

Example:

smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem

This feature is available in Postfix 2.2 and later.


(default: empty)

File with DH parameters that the Postfix SMTP server should
use with export-grade EDH ciphers. The default SMTP server cipher
grade is “medium” with Postfix releases after the middle of 2022,
and as a result export-grade cipher suites are by default not used.

With Postfix ≥ 3.6 export-grade Diffie-Hellman key exchange
is no longer supported, and this parameter is silently ignored.

See also the discussion under the smtpd_tls_dh1024_param_file
configuration parameter.

Example:

smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

This feature is available in Postfix 2.2 and later,
but is ignored in Postfix 3.6 and later.


(default: $smtpd_tls_dcert_file)

File with the Postfix SMTP server DSA private key in PEM format.
This file may be combined with the Postfix SMTP server DSA certificate
file specified with $smtpd_tls_dcert_file. The DSA algorithm is obsolete
and should not be used.

The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account (“root”), and no access
to anyone else.

This feature is available in Postfix 2.2 and later.


(default: empty)

File with the Postfix SMTP server ECDSA certificate in PEM format.
This file may also contain the Postfix SMTP server private ECDSA key.
With Postfix ≥ 3.4 the preferred way to configure server keys and
certificates is via the “smtpd_tls_chain_files” parameter.

See the discussion under smtpd_tls_cert_file for more details.

Example:

smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.


(default: $smtpd_tls_eccert_file)

File with the Postfix SMTP server ECDSA private key in PEM format.
This file may be combined with the Postfix SMTP server ECDSA certificate
file specified with $smtpd_tls_eccert_file. With Postfix ≥ 3.4 the
preferred way to configure server keys and certificates is via the
smtpd_tls_chain_files” parameter.

The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account (“root”), and no access
to anyone else.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.


(default: see “postconf -d” output)

The Postfix SMTP server security grade for ephemeral elliptic-curve
Diffie-Hellman (EECDH) key exchange. As of Postfix 3.6, the value of
this parameter is always ignored, and Postfix behaves as though the
auto value (described below) was chosen.

The available choices are:

auto
Use the most preferred curve that is
supported by both the client and the server. This setting requires
Postfix ≥ 3.2 compiled and linked with OpenSSL ≥ 1.0.2. This
is the default setting under the above conditions (and the only
setting used with Postfix ≥ 3.6).
none
Don’t use EECDH. Ciphers based on EECDH key
exchange will be disabled. This is the default in Postfix versions
2.6 and 2.7.
strong
Use EECDH with approximately 128 bits of
security at a reasonable computational cost. This is the default in
Postfix versions 2.8–3.5.
ultra
Use EECDH with approximately 192 bits of
security at computational cost that is approximately twice as high
as 128 bit strength ECC.

If you want to take maximal advantage of ciphers that offer forward secrecy see
the Getting
started
section of FORWARD_SECRECY_README. The
full document conveniently presents all information about Postfix
“perfect” forward secrecy support in one place: what forward secrecy
is, how to tweak settings, and what you can expect to see when
Postfix uses ciphers with forward secrecy.

This feature is available in Postfix 2.6 and later, when it is
compiled and linked with OpenSSL 1.0.0 or later on platforms
where EC algorithms have not been disabled by the vendor.


(default: empty)

List of ciphers or cipher types to exclude from the SMTP server
cipher list at all TLS security levels. Excluding valid ciphers
can create interoperability problems. DO NOT exclude ciphers unless it
is essential to do so. This is not an OpenSSL cipherlist; it is a simple
list separated by whitespace and/or commas. The elements are a single
cipher, or one or more ” ” separated cipher properties, in which case
only ciphers matching all the properties are excluded.

Examples (some of these will cause problems):

smtpd_tls_exclude_ciphers = aNULL
smtpd_tls_exclude_ciphers = MD5, DES
smtpd_tls_exclude_ciphers = DES MD5
smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtpd_tls_exclude_ciphers = kEDH aRSA

The first setting disables anonymous ciphers. The next setting
disables ciphers that use the MD5 digest algorithm or the (single) DES
encryption algorithm. The next setting disables ciphers that use MD5 and
DES together. The next setting disables the two ciphers “AES256-SHA”
and “DES-CBC3-MD5”. The last setting disables ciphers that use “EDH”
key exchange with RSA authentication.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The message digest algorithm to construct remote SMTP client-certificate
fingerprints or public key fingerprints (Postfix 2.9 and later) for
check_ccert_access and permit_tls_clientcerts.

The default algorithm is sha256 with Postfix ≥ 3.6
and the compatibility_level set to 3.6 or higher. With Postfix
≤ 3.5, the default algorithm is md5.

The best-practice algorithm is now sha256. Recent advances in hash
function cryptanalysis have led to md5 and sha1 being deprecated in favor of
sha256. However, as long as there are no known “second pre-image” attacks
against the older algorithms, their use in this context, though not
recommended, is still likely safe.

While additional digest algorithms are often available with OpenSSL’s
libcrypto, only those used by libssl in SSL cipher suites are available to
Postfix. You’ll likely find support for md5, sha1, sha256 and sha512.

To find the fingerprint of a specific certificate file, with a
specific digest algorithm, run:

$ openssl x509 -noout -fingerprint -digest -in certfile.pem

The text to the right of “=” sign is the desired fingerprint.
For example:

$ openssl x509 -noout -fingerprint -sha256 -in cert.pem
SHA256 Fingerprint=D4:6A:AB:19:24:...:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

To extract the public key fingerprint from an X.509 certificate,
you need to extract the public key from the certificate and compute
the appropriate digest of its DER (ASN.1) encoding. With OpenSSL
the “-pubkey” option of the “x509” command extracts the public
key always in “PEM” format. We pipe the result to another OpenSSL
command that converts the key to DER and then to the “dgst” command
to compute the fingerprint.

Example:

$ openssl x509 -in cert.pem -noout -pubkey |
    openssl pkey -pubin -outform DER |
    openssl dgst -sha256 -c
(stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

The Postfix SMTP server and client log the peer (leaf) certificate
fingerprint and public key fingerprint when the TLS loglevel is 2 or
higher.

Example: client-certificate access table, with sha256 fingerprints:

/etc/postfix/main.cf:
    smtpd_tls_fingerprint_digest = sha256
    smtpd_client_restrictions =
        check_ccert_accesshash:/etc/postfix/access,
        reject
/etc/postfix/access:
    # Action folded to next line...
    AF:88:7C:AD:51:95:6F:36:96:...:01:FB:2E:48:CD:AB:49:25:A2:3B
        OK
    85:16:78:FD:73:6E:CE:70:E0:...:5F:0D:3C:C8:6D:C4:2C:24:59:E1
        permit_auth_destination

This feature is available in Postfix 2.5 and later.


(default: $smtpd_tls_cert_file)

File with the Postfix SMTP server RSA private key in PEM format.
This file may be combined with the Postfix SMTP server RSA certificate
file specified with $smtpd_tls_cert_file. With Postfix ≥ 3.4 the
preferred way to configure server keys and certificates is via the
smtpd_tls_chain_files” parameter.

The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account (“root”), and no access
to anyone else.


(default: 0)

Enable additional Postfix SMTP server logging of TLS activity.
Each logging level also includes the information that is logged at
a lower logging level.

0 Disable logging of TLS activity.
1 Log only a summary message on TLS handshake completion
— no logging of client certificate trust-chain verification errors
if client certificate verification is not required. With Postfix 2.8 and
earlier, log the summary message, peer certificate summary information
and unconditionally log trust-chain verification errors.
2 Also log levels during TLS negotiation.
3 Also log hexadecimal and ASCII dump of TLS negotiation
process.
4 Also log hexadecimal and ASCII dump of complete
transmission after STARTTLS.

Do not use “smtpd_tls_loglevel = 2″ or higher except in case
of problems. Use of loglevel 4 is strongly discouraged.

This feature is available in Postfix 2.2 and later.


(default: medium)

The minimum TLS cipher grade that the Postfix SMTP server will
use with mandatory TLS encryption. The default grade (“medium”) is
sufficiently strong that any benefit from globally restricting TLS
sessions to a more stringent grade is likely negligible, especially
given the fact that many implementations still do not offer any stronger
(“high” grade) ciphers, while those that do, will always use “high”
grade ciphers. So insisting on “high” grade ciphers is generally
counter-productive. Allowing “export” or “low” ciphers is typically
not a good idea, as systems limited to just these are limited to
obsolete browsers. No known SMTP clients fail to support at least
one “medium” or “high” grade cipher.

The following cipher grades are supported:

export
Enable “EXPORT” grade or stronger OpenSSL ciphers. The
underlying cipherlist is specified via the tls_export_cipherlist
configuration parameter, which you are strongly encouraged not to
change. This choice is insecure and SHOULD NOT be used.
low
Enable “LOW” grade or stronger OpenSSL ciphers. The underlying
cipherlist is specified via the tls_low_cipherlist configuration
parameter, which you are strongly encouraged not to change. This
choice is insecure and SHOULD NOT be used.
medium
Enable “MEDIUM” grade or stronger OpenSSL ciphers. These use 128-bit
or longer symmetric bulk-encryption keys. This is the default minimum
strength for mandatory TLS encryption. The underlying cipherlist is
specified via the tls_medium_cipherlist configuration parameter, which
you are strongly encouraged not to change.
high
Enable only “HIGH” grade OpenSSL ciphers. The
underlying cipherlist is specified via the tls_high_cipherlist
configuration parameter, which you are strongly encouraged to
not change.
null
Enable only the “NULL” OpenSSL ciphers, these provide authentication
without encryption. This setting is only appropriate in the rare
case that all clients are prepared to use NULL ciphers (not normally
enabled in TLS clients). The underlying cipherlist is specified via the
tls_null_cipherlist configuration parameter, which you are strongly
encouraged not to change.

Cipher types listed in
smtpd_tls_mandatory_exclude_ciphers or smtpd_tls_exclude_ciphers are
excluded from the base definition of the selected cipher grade. See
smtpd_tls_ciphers for cipher controls that apply to opportunistic
TLS.

The underlying cipherlists for grades other than “null” include
anonymous ciphers, but these are automatically filtered out if the
server is configured to ask for remote SMTP client certificates. You are very
unlikely to need to take any steps to exclude anonymous ciphers, they
are excluded automatically as required. If you must exclude anonymous
ciphers even when Postfix does not need or use peer certificates, set
smtpd_tls_exclude_ciphers = aNULL”. To exclude anonymous ciphers only
when TLS is enforced, set “smtpd_tls_mandatory_exclude_ciphers = aNULL”.

This feature is available in Postfix 2.3 and later.


(default: empty)

Additional list of ciphers or cipher types to exclude from the
Postfix SMTP server cipher list at mandatory TLS security levels.
This list
works in addition to the exclusions listed with smtpd_tls_exclude_ciphers
(see there for syntax details).

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

TLS protocols accepted by the Postfix SMTP server with mandatory TLS
encryption. If the list is empty, the server supports all available TLS
protocol versions. A non-empty value is a list of protocol names to
include or exclude, separated by whitespace, commas or colons.

The valid protocol names (see SSL_get_version(3)) are “SSLv2”,
“SSLv3”, “TLSv1”, “TLSv1.1”, “TLSv1.2” and “TLSv1.3”. Starting with
Postfix 3.6, the default value is “>=TLSv1”, which sets TLS 1.0 as
the lowest supported TLS protocol version (see below). Older releases
use the “!” exclusion syntax, also described below.

As of Postfix 3.6, the preferred way to limit the range of
acceptable protocols is to set the lowest acceptable TLS protocol
version and/or the highest acceptable TLS protocol version. To set the
lower bound include an element of the form: “>=version” where
version is a either one of the TLS protocol names listed above,
or a hexadecimal number corresponding to the desired TLS protocol
version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.). For the upper
bound, use “<=version“. There must be no whitespace between
the “>=” or “<=” symbols and the protocol name or number.

Hexadecimal protocol numbers make it possible to specify protocol
bounds for TLS versions that are known to OpenSSL, but might not be
known to Postfix. They cannot be used with the legacy exclusion syntax.
Leading “0” or “0x” prefixes are supported, but not required.
Therefore, “301”, “0301”, “0x301” and “0x0301” are all equivalent to
“TLSv1”. Hexadecimal versions unknown to OpenSSL will fail to set the
upper or lower bound, and a warning will be logged. Hexadecimal
versions should only be used when Postfix is linked with some future
version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
yet support a symbolic name for that protocol version.

Hexadecimal example (Postfix ≥ 3.6):

# Allow only TLS 1.2 through (hypothetical) TLS 1.4, once supported
# in some future version of OpenSSL (presently a warning is logged).
smtpd_tls_mandatory_protocols = >=TLSv1.2, <=0305
# Allow only TLS 1.2 and up:
smtpd_tls_mandatory_protocols = >=0x0303

With Postfix < 3.6 there is no support for a minimum or maximum
version, and the protocol range is configured via protocol exclusions.
To require at least TLS 1.0, set “smtpd_tls_mandatory_protocols =
!SSLv2, !SSLv3″. Listing the protocols to include, rather than
protocols to exclude, is supported, but not recommended. The exclusion
form more accurately matches the underlying OpenSSL interface.

Support for “TLSv1.3” was introduced in OpenSSL 1.1.1. Disabling
this protocol via “!TLSv1.3” is supported since Postfix 3.4 (or patch
releases ≥ 3.0.14, 3.1.10, 3.2.7 and 3.3.2).

Example:

# Preferred syntax with Postfix ≥ 3.6:
smtpd_tls_mandatory_protocols = >=TLSv1.2, <=TLSv1.3
# Legacy syntax:
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1

This feature is available in Postfix 2.3 and later.


(default: see postconf -d output)

TLS protocols accepted by the Postfix SMTP server with opportunistic
TLS encryption. If the list is empty, the server supports all available
TLS protocol versions. A non-empty value is a list of protocol names to
include or exclude, separated by whitespace, commas or colons.

The valid protocol names (see SSL_get_version(3)) are “SSLv2”,
“SSLv3”, “TLSv1”, “TLSv1.1”, “TLSv1.2” and “TLSv1.3”. Starting with
Postfix 3.6, the default value is “>=TLSv1”, which sets TLS 1.0 as
the lowest supported TLS protocol version (see below). Older releases
use the “!” exclusion syntax, also described below.

As of Postfix 3.6, the preferred way to limit the range of
acceptable protocols is to set the lowest acceptable TLS protocol
version and/or the highest acceptable TLS protocol version. To set the
lower bound include an element of the form: “>=version” where
version is a either one of the TLS protocol names listed above,
or a hexadecimal number corresponding to the desired TLS protocol
version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.). For the upper
bound, use “<=version“. There must be no whitespace between
the “>=” or “<=” symbols and the protocol name or number.

Hexadecimal protocol numbers make it possible to specify protocol
bounds for TLS versions that are known to OpenSSL, but might not be
known to Postfix. They cannot be used with the legacy exclusion syntax.
Leading “0” or “0x” prefixes are supported, but not required.
Therefore, “301”, “0301”, “0x301” and “0x0301” are all equivalent to
“TLSv1”. Hexadecimal versions unknown to OpenSSL will fail to set the
upper or lower bound, and a warning will be logged. Hexadecimal
versions should only be used when Postfix is linked with some future
version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
yet support a symbolic name for that protocol version.

Hexadecimal example (Postfix ≥ 3.6):

# Allow only TLS 1.0 through (hypothetical) TLS 1.4, once supported
# in some future version of OpenSSL (presently a warning is logged).
smtpd_tls_protocols = >=TLSv1, <=0305
# Allow only TLS 1.0 and up:
smtpd_tls_protocols = >=0x0301

With Postfix < 3.6 there is no support for a minimum or maximum
version, and the protocol range is configured via protocol exclusions.
To require at least TLS 1.0, set “smtpd_tls_protocols = !SSLv2, !SSLv3″.
Listing the protocols to include, rather than protocols to exclude, is
supported, but not recommended. The exclusion form more accurately
matches the underlying OpenSSL interface.

Support for “TLSv1.3” was introduced in OpenSSL 1.1.1. Disabling
this protocol via “!TLSv1.3” is supported since Postfix 3.4 (or patch
releases ≥ 3.0.14, 3.1.10, 3.2.7 and 3.3.2).

Example:

# Preferred syntax with Postfix ≥ 3.6:
smtpd_tls_protocols = >=TLSv1, <=TLSv1.3
# Legacy syntax:
smtpd_tls_protocols = !SSLv2, !SSLv3

This feature is available in Postfix 2.6 and later.


(default: no)

Request that the Postfix SMTP server produces Received: message
headers that include information about the protocol and cipher used,
as well as the remote SMTP client CommonName and client certificate issuer
CommonName. This is disabled by default, as the information may
be modified in transit through other mail servers. Only information
that was recorded by the final destination can be trusted.

This feature is available in Postfix 2.2 and later.


(default: no)

With mandatory TLS encryption, require a trusted remote SMTP client
certificate in order to allow TLS connections to proceed. This
option implies “smtpd_tls_ask_ccert = yes”.

When TLS encryption is optional, this setting is ignored with
a warning written to the mail log.

This feature is available in Postfix 2.2 and later.


(default: empty)

The SMTP TLS security level for the Postfix SMTP server; when
a non-empty value is specified, this overrides the obsolete parameters
smtpd_use_tls and smtpd_enforce_tls. This parameter is ignored with
smtpd_tls_wrappermode = yes”.

Specify one of the following security levels:

none
TLS will not be used.
may
Opportunistic TLS: announce STARTTLS support
to remote SMTP clients, but do not require that clients use TLS encryption.
encrypt
Mandatory TLS encryption: announce
STARTTLS support to remote SMTP clients, and require that clients use TLS
encryption. According to RFC 2487 this MUST NOT be applied in case
of a publicly-referenced SMTP server. Instead, this option should
be used only on dedicated servers.

Note 1: the “fingerprint”, “verify” and “secure” levels are not
supported here.
The Postfix SMTP server logs a warning and uses “encrypt” instead.
To verify remote SMTP client certificates, see TLS_README for a discussion
of the smtpd_tls_ask_ccert, smtpd_tls_req_ccert, and permit_tls_clientcerts
features.

Note 2: The parameter setting “smtpd_tls_security_level =
encrypt” implies “smtpd_tls_auth_only = yes”.

Note 3: when invoked via “sendmail -bs”, Postfix will never
offer STARTTLS due to insufficient privileges to access the server
private key. This is intended behavior.

This feature is available in Postfix 2.3 and later.


(default: empty)

Name of the file containing the optional Postfix SMTP server
TLS session cache. Specify a database type that supports enumeration,
such as btree or sdbm; there is no need to support
concurrent access. The file is created if it does not exist. The smtpd(8)
daemon does not use this parameter directly, rather the cache is
implemented indirectly in the tlsmgr(8) daemon. This means that
per-smtpd-instance master.cf overrides of this parameter are not
effective. Note that each of the cache databases supported by tlsmgr(8)
daemon: $smtpd_tls_session_cache_database, $smtp_tls_session_cache_database
(and with Postfix 2.3 and later $lmtp_tls_session_cache_database), needs to be
stored separately. It is not at this time possible to store multiple
caches in a single database.

Note: dbm databases are not suitable. TLS
session objects are too large.

As of version 2.5, Postfix no longer uses root privileges when
opening this file. The file should now be stored under the Postfix-owned
data_directory. As a migration aid, an attempt to open the file
under a non-Postfix directory is redirected to the Postfix-owned
data_directory, and a warning is logged.

As of Postfix 2.11 the preferred mechanism for session resumption
is RFC 5077 TLS session tickets, which don’t require server-side
storage. Consequently, for Postfix ≥ 2.11 this parameter should
generally be left empty. TLS session tickets require an OpenSSL
library (at least version 0.9.8h) that provides full support for
this TLS extension. See also smtpd_tls_session_cache_timeout.

Example:

smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache

This feature is available in Postfix 2.2 and later.


(default: 3600s)

The expiration time of Postfix SMTP server TLS session cache
information. A cache cleanup is performed periodically
every $smtpd_tls_session_cache_timeout seconds. As with
$smtpd_tls_session_cache_database, this parameter is implemented in the
tlsmgr(8) daemon and therefore per-smtpd-instance master.cf overrides
are not possible.

As of Postfix 2.11 this setting cannot exceed 100 days. If set
≤ 0, session caching is disabled, not just via the database, but
also via RFC 5077 TLS session tickets, which don’t require server-side
storage. If set to a positive value less than 2 minutes, the minimum
value of 2 minutes is used instead. TLS session tickets require
an OpenSSL library (at least version 0.9.8h) that provides full
support for this TLS extension.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.2 and later, and updated
for TLS session ticket support in Postfix 2.11.


(default: no)

Run the Postfix SMTP server in TLS “wrapper” mode,
instead of using the STARTTLS command.

If you want to support this service, enable a special port in
master.cf, and specify “-o smtpd_tls_wrappermode=yes” on the SMTP
server’s command line. Port 465 (submissions/smtps) is reserved for
this purpose.

This feature is available in Postfix 2.2 and later.


(default: empty)

The name of the proxy protocol used by an optional before-smtpd
proxy agent. When a proxy agent is used, this protocol conveys local
and remote address and port information. Specify
smtpd_upstream_proxy_protocol = haproxy” to enable the haproxy
protocol; version 2 is supported with Postfix 3.5 and later.

NOTE: To use the nginx proxy with smtpd(8), enable the XCLIENT
protocol with smtpd_authorized_xclient_hosts. This supports SASL
authentication in the proxy agent (Postfix 2.9 and later).

This feature is available in Postfix 2.10 and later.


(default: 5s)

The time limit for the proxy protocol specified with the
smtpd_upstream_proxy_protocol parameter.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.10 and later.


(default: no)

Opportunistic TLS: announce STARTTLS support to remote SMTP clients,
but do not require that clients use TLS encryption.

Note: when invoked via “sendmail -bs“, Postfix will never offer
STARTTLS due to insufficient privileges to access the server private
key. This is intended behavior.

This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtpd_tls_security_level instead.


(default: sendmail, verify)

Detect that a message requires SMTPUTF8 support for the specified
mail origin classes. This is a workaround to avoid chicken-and-egg
problems during the initial SMTPUTF8 roll-out in environments with
pre-existing mail flows that contain UTF8. Those mail flows should
not break because Postfix suddenly refuses to deliver such mail
to down-stream MTAs that don’t announce SMTPUTF8 support.

The problem is that Postfix cannot rely solely on the sender’s
declaration that a message requires SMTPUTF8 support, because UTF8
may be introduced during local processing (for example, the client
hostname in Postfix’s Received: header, adding @$myorigin or
.$mydomain to an incomplete address, address rewriting, alias
expansion, automatic BCC recipients, local forwarding, and changes
made by header checks or Milter applications).

For now, the default is to enable “SMTPUTF8 required” autodetection
only for Postfix sendmail command-line submissions and address
verification probes. This may change once SMTPUTF8 support achieves
world domination. However, sites that add UTF8 content via local
processing (see above) should autodetect the need for SMTPUTF8
support for all email.

Specify one or more of the following:

sendmail
Submission with the Postfix
sendmail(1) command.
smtpd
Mail received with the smtpd(8)
daemon.
qmqpd
Mail received with the qmqpd(8)
daemon.
forward
Local forwarding or aliasing. When
a message is received with “SMTPUTF8 required”, then the forwarded
(aliased) message always has “SMTPUTF8 required”.
bounce
Submission by the bounce(8) daemon.
When a message is received with “SMTPUTF8 required”, then the
delivery status notification always has “SMTPUTF8 required”.
notify
Postmaster notification from the
smtp(8) or smtpd(8) daemon.
verify
Address verification probe from the
verify(8) daemon.
all
Enable SMTPUTF8 autodetection for all
mail.

This feature is available in Postfix 3.0 and later.


(default: yes)

Enable preliminary SMTPUTF8 support for the protocols described
in RFC 6531, RFC 6532, and RFC 6533. This requires that Postfix is
built to support these protocols.

This feature is available in Postfix 3.0 and later.


(default: no)

Safety net to keep mail queued that would otherwise be returned to
the sender. This parameter disables locally-generated bounces,
changes the handling of negative responses from remote servers,
content filters or plugins,
and prevents the Postfix SMTP server from rejecting mail permanently
by changing 5xx reply codes into 4xx. However, soft_bounce is no
cure for address rewriting mistakes or mail routing mistakes.

Note: “soft_bounce = yes” is in some cases implemented by modifying
server responses. Therefore, the response that Postfix logs may
differ from the response that Postfix actually sends or receives.

Example:

soft_bounce = yes

(default: 500s)

The time after which a stale exclusive mailbox lockfile is removed.
This is used for delivery to file or mailbox.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: empty)

This feature is documented in the STRESS_README document.

This feature is available in Postfix 2.5 and later.


(default: no)

Reject mail with 8-bit text in message headers. This blocks mail
from poorly written applications.

This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.

This feature is available in Postfix 2.0 and later.


(default: no)

Enable both strict_7bit_headers and strict_8bitmime_body.

This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.

This feature is available in Postfix 2.0 and later.


(default: no)

Reject 8-bit message body text without 8-bit MIME content encoding
information. This blocks mail from poorly written applications.

Unfortunately, this also rejects majordomo approval requests when
the included request contains valid 8-bit MIME mail, and it rejects
bounces from mailers that do not MIME encapsulate 8-bit content
(for example, bounces from qmail or from old versions of Postfix).

This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.

This feature is available in Postfix 2.0 and later.


(default: yes)

Defer delivery when a mailbox file is not owned by its recipient.
The default setting is not backwards compatible.

This feature is available in Postfix 2.5.3 and later.


(default: no)

Reject mail with invalid Content-Transfer-Encoding: information
for the message/* or multipart/* MIME content types. This blocks
mail from poorly written software.

This feature should not be enabled on a general purpose mail server,
because it will reject mail after a single violation.

This feature is available in Postfix 2.0 and later.


(default: no)

Require that addresses received in SMTP MAIL FROM and RCPT TO
commands are enclosed with <>, and that those addresses do
not contain RFC 822 style comments or phrases. This stops mail
from poorly written software.

By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL
FROM and RCPT TO addresses.


(default: no)

Enable stricter enforcement of the SMTPUTF8 protocol. The Postfix
SMTP server accepts UTF8 sender or recipient addresses only when
the client requests an SMTPUTF8 mail transaction.

This feature is available in Postfix 3.0 and later.


(default: no)

Obsolete SUN mailtool compatibility feature. Instead, use
mailbox_delivery_lock = dotlock”.


(default: yes)

Enable the rewriting of “site!user” into “user@site”. This is
necessary if your machine is connected to UUCP networks. It is
enabled by default.

Note: with Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true:

To get the behavior before Postfix version 2.2, specify
local_header_rewrite_clients = static:all”.

Example:

swap_bangpath = no

(default: mail)

The syslog facility of Postfix logging. Specify a facility as
defined in syslog.conf(5). The default facility is “mail”.

Warning: a non-default syslog_facility setting takes effect only
after a Postfix process has completed initialization. Errors during
process initialization will be logged with the default facility.
Examples are errors while parsing the command line arguments, and
errors while accessing the Postfix main.cf configuration file.


(default: see “postconf -d” output)

A prefix that is prepended to the process name in syslog
records, so that, for example, “smtpd” becomes “prefix/smtpd”.

Warning: a non-default syslog_name setting takes effect only after
a Postfix process has completed initialization. Errors during
process initialization will be logged with the default name. Examples
are errors while parsing the command line arguments, and errors
while accessing the Postfix main.cf configuration file.


(default: 0)

An optional workaround for routers that break TCP window scaling.
Specify a value > 0 and < 65536 to enable this feature. With
Postfix TCP servers (smtpd(8), qmqpd(8)), this feature is implemented
by the Postfix master(8) daemon.

To change this parameter without stopping Postfix, you need to
first terminate all Postfix TCP servers:

# postconf -e master_service_disable=inet
# postfix reload

This immediately terminates all processes that accept network
connections. Next, you enable Postfix TCP servers with the updated
tcp_windowsize setting:

# postconf -e tcp_windowsize=65535 master_service_disable=
# postfix reload

If you skip these steps with a running Postfix system, then the
tcp_windowsize change will work only for Postfix TCP clients (smtp(8),
lmtp(8)).

This feature is available in Postfix 2.6 and later.


(default: no)

Append the system-supplied default Certification Authority
certificates to the ones specified with *_tls_CApath or *_tls_CAfile.
The default is “no”; this prevents Postfix from trusting third-party
certificates and giving them relay permission with
permit_tls_all_clientcerts.

This feature is available in Postfix 2.4.15, 2.5.11, 2.6.8,
2.7.2 and later versions. Specify “tls_append_default_CA = yes” for
backwards compatibility, to avoid breaking certificate verification
with sites that don’t use permit_tls_all_clientcerts.


(default: 32)

The number of pseudo-random bytes that an smtp(8) or smtpd(8)
process requests from the tlsmgr(8) server in order to seed its
internal pseudo random number generator (PRNG). The default of 32
bytes (equivalent to 256 bits) is sufficient to generate a 128bit
(or 168bit) session key.

This feature is available in Postfix 2.2 and later.


(default: on)

Configure RFC7671 DANE TLSA digest algorithm agility.
Do not change this setting from its default value.

See Section 8 of RFC7671 for correct key rotation procedures.

This feature is available in Postfix 2.11 through 3.1. Postfix
3.2 and later ignore this configuration parameter and behave as
though it were set to “on”.


(default: sha512 sha256)

DANE TLSA (RFC 6698, RFC 7671, RFC 7672) resource-record “matching
type” digest algorithms in descending preference order. All the
specified algorithms must be supported by the underlying OpenSSL
library, otherwise the Postfix SMTP client will not support DANE
TLSA security.

Specify a list of digest names separated by commas and/or
whitespace. Each digest name may be followed by an optional
“=<number>” suffix. For example, “sha512” may instead be specified
as “sha512=2” and “sha256” may instead be specified as “sha256=1”.
The optional number must match the IANA assigned TLSA matching type number the algorithm in question.
Postfix will check this constraint for the algorithms it knows about.
Additional matching type algorithms registered with IANA can be added
with explicit numbers provided they are supported by OpenSSL.

Invalid list elements are logged with a warning and disable DANE
support. TLSA RRs that specify digests not included in the list are
ignored with a warning.

Note: It is unwise to omit sha256 from the digest list. This
digest algorithm is the only mandatory to implement digest algorithm
in RFC 6698, and many servers are expected to publish TLSA records
with just sha256 digests. Unless one of the standard digests is
seriously compromised and servers have had ample time to update their
TLSA records you should not omit any standard digests, just arrange
them in order from strongest to weakest.

This feature is available in Postfix 2.11 and later.


(default: yes)

Enable support for RFC 6698 (DANE TLSA) DNS records that contain
digests of trust-anchors with certificate usage “2”. Do not change
this setting from its default value.

This feature is available in Postfix 2.11 through 3.1. It has
been withdrawn in Postfix 3.2, as trust-anchor TLSA records are now
widely used and have proved sufficiently reliable. Postfix 3.2 and
later ignore this configuration parameter and behaves as though it
were set to “yes”.


(default: see “postconf -d” output)

List or bit-mask of OpenSSL bug work-arounds to disable.

The OpenSSL toolkit includes a set of work-arounds for buggy SSL/TLS
implementations. Applications, such as Postfix, that want to maximize
interoperability ask the OpenSSL library to enable the full set of
recommended work-arounds.

From time to time, it is discovered that a work-around creates a
security issue, and should no longer be used. If upgrading OpenSSL
to a fixed version is not an option or an upgrade is not available
in a timely manner, or in closed environments where no buggy clients
or servers exist, it may be appropriate to disable some or all of the
OpenSSL interoperability work-arounds. This parameter specifies which
bug work-arounds to disable.

If the value of the parameter is a hexadecimal long integer starting
with “0x”, the bug work-arounds corresponding to the bits specified in
its value are removed from the SSL_OP_ALL work-around bit-mask
(see openssl/ssl.h and SSL_CTX_set_options(3)). You can specify more
bits than are present in SSL_OP_ALL, excess bits are ignored. Specifying
0xFFFFFFFF disables all bug-workarounds on a 32-bit system. This should
also be sufficient on 64-bit systems, until OpenSSL abandons support
for 32-bit systems and starts using the high 32 bits of a 64-bit
bug-workaround mask.

Otherwise, the parameter is a white-space or comma separated list
of specific named bug work-arounds chosen from the list below. It
is possible that your OpenSSL version includes new bug work-arounds
added after your Postfix source code was last updated, in that case
you can only disable one of these via the hexadecimal syntax above.

CRYPTOPRO_TLSEXT_BUG
New with GOST support in
OpenSSL 1.0.0.
DONT_INSERT_EMPTY_FRAGMENTS
See
SSL_CTX_set_options(3)
LEGACY_SERVER_CONNECT
See SSL_CTX_set_options(3)
MICROSOFT_BIG_SSLV3_BUFFER
See
SSL_CTX_set_options(3)
MICROSOFT_SESS_ID_BUG
See SSL_CTX_set_options(3)
MSIE_SSLV2_RSA_PADDING
also aliased as
CVE-2005-2969. Postfix 2.8 disables this work-around by
default with OpenSSL versions that may predate the fix. Fixed in
OpenSSL 0.9.7h and OpenSSL 0.9.8a.
NETSCAPE_CHALLENGE_BUG
See SSL_CTX_set_options(3)
NETSCAPE_REUSE_CIPHER_CHANGE_BUG
also aliased
as CVE-2022-4180. Postfix 2.8 disables this work-around by
default with OpenSSL versions that may predate the fix. Fixed in
OpenSSL 0.9.8q and OpenSSL 1.0.0c.
SSLEAY_080_CLIENT_DH_BUG
See
SSL_CTX_set_options(3)
SSLREF2_REUSE_CERT_TYPE_BUG
See
SSL_CTX_set_options(3)
TLS_BLOCK_PADDING_BUG
See SSL_CTX_set_options(3)
TLS_D5_BUG
See SSL_CTX_set_options(3)
TLS_ROLLBACK_BUG
See SSL_CTX_set_options(3).
This is disabled in OpenSSL 0.9.7 and later. Nobody should still
be using 0.9.6!
TLSEXT_PADDING
Postfix ≥ 3.4. See SSL_CTX_set_options(3).

This feature is available in Postfix 2.8 and later.


(default: see “postconf -d” output)

The prioritized list of elliptic curves supported by the Postfix
SMTP client and server. These curves are used by the Postfix SMTP
server when “smtpd_tls_eecdh_grade = auto”. The selected curves
must be implemented by OpenSSL and be standardized for use in TLS
(RFC 8422). It is unwise to list only
“bleeding-edge” curves supported by a small subset of clients. The
default list is suitable for most users.

Postfix skips curve names that are unknown to OpenSSL, or that
are known but not yet implemented. This makes it possible to
“anticipate” support for curves that should be used once they become
available. In particular, in some OpenSSL versions, the new RFC8031 curves “X25519” and “X448” may be known by name, but ECDH
support for either or both may be missing. These curves may appear
in the default value of this parameter, even though they’ll only
be usable with later versions of OpenSSL.

This feature is available in Postfix 3.2 and later, when it is
compiled and linked with OpenSSL 1.0.2 or later on platforms where
EC algorithms have not been disabled by the vendor.


(default: prime256v1)

The elliptic curve used by the Postfix SMTP server for sensibly
strong
ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
server when “smtpd_tls_eecdh_grade = strong”. The phrase “sensibly
strong” means approximately 128-bit security based on best known
attacks. The selected curve must be implemented by OpenSSL (as
reported by ecparam(1) with the “-list_curves” option) and be one
of the curves listed in Section 5.1.1 of RFC 8422. You should not
generally change this setting. Remote SMTP client implementations
must support this curve for EECDH key exchange to take place. It
is unwise to choose only “bleeding-edge” curves supported by only a
small subset of clients.

The default “strong” curve is rated in NSA Suite
B
for information classified up to SECRET.

Note: elliptic curve names are poorly standardized; different
standards groups are assigning different names to the same underlying
curves. The curve with the X9.62 name “prime256v1” is also known
under the SECG name “secp256r1”, but OpenSSL does not recognize the
latter name.

If you want to take maximal advantage of ciphers that offer forward secrecy see
the Getting
started
section of FORWARD_SECRECY_README. The
full document conveniently presents all information about Postfix
“perfect” forward secrecy support in one place: what forward secrecy
is, how to tweak settings, and what you can expect to see when
Postfix uses ciphers with forward secrecy.

This feature is available in Postfix 2.6 and later, when it is
compiled and linked with OpenSSL 1.0.0 or later on platforms where
EC algorithms have not been disabled by the vendor.


(default: secp384r1)

The elliptic curve used by the Postfix SMTP server for maximally
strong
ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
server when “smtpd_tls_eecdh_grade = ultra”. The phrase “maximally
strong” means approximately 192-bit security based on best known attacks.
This additional strength comes at a significant computational cost, most
users should instead set “smtpd_tls_eecdh_grade = strong”. The selected
curve must be implemented by OpenSSL (as reported by ecparam(1) with the
“-list_curves” option) and be one of the curves listed in Section 5.1.1
of RFC 8422. You should not generally change this setting. Remote SMTP
client implementations must support this curve for EECDH key exchange
to take place. It is unwise to choose only “bleeding-edge” curves
supported by only a small subset of clients.

This default “ultra” curve is rated in NSA Suite
B
for information classified up to TOP SECRET.

If you want to take maximal advantage of ciphers that offer forward secrecy see
the Getting
started
section of FORWARD_SECRECY_README. The
full document conveniently presents all information about Postfix
“perfect” forward secrecy support in one place: what forward secrecy
is, how to tweak settings, and what you can expect to see when
Postfix uses ciphers with forward secrecy.

This feature is available in Postfix 2.6 and later, when it is
compiled and linked with OpenSSL 1.0.0 or later on platforms where
EC algorithms have not been disabled by the vendor.


(default: see “postconf -d” output)

The OpenSSL cipherlist for “export” or higher grade ciphers. This
defines the meaning of the “export” setting in smtpd_tls_ciphers,
smtpd_tls_mandatory_ciphers, smtp_tls_ciphers, smtp_tls_mandatory_ciphers,
lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers. With Postfix
releases before the middle of 2022 this is the default cipherlist
for the opportunistic (“may”) TLS client security level and also
the default cipherlist for the SMTP server. You are strongly
encouraged not to change this setting.

This feature is available in Postfix 2.3 and later.


(default: yes)

A workaround for implementations that hang Postfix while shutting
down a TLS session, until Postfix times out. With this enabled,
Postfix will not wait for the remote TLS peer to respond to a TLS
‘close’ notification. This behavior is recommended for TLSv1.0 and
later.


(default: see “postconf -d” output)

The OpenSSL cipherlist for “high” grade ciphers. This defines
the meaning of the “high” setting in smtpd_tls_ciphers,
smtpd_tls_mandatory_ciphers, smtp_tls_ciphers, smtp_tls_mandatory_ciphers,
lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers. You are strongly
encouraged not to change this setting.

This feature is available in Postfix 2.3 and later.


(default: no)

A temporary migration aid for sites that use certificate
public-key fingerprints with Postfix 2.9.0..2.9.5, which use
an incorrect algorithm. This parameter has no effect on the certificate
fingerprint support that is available since Postfix 2.2.

Specify “tls_legacy_public_key_fingerprints = yes” temporarily,
pending a migration from configuration files with incorrect Postfix
2.9.0..2.9.5 certificate public-key finger prints, to the correct
fingerprints used by Postfix 2.9.6 and later. To compute the correct
certificate public-key fingerprints, see TLS_README.

This feature is available in Postfix 2.9.6 and later.


(default: see “postconf -d” output)

The OpenSSL cipherlist for “low” or higher grade ciphers. This defines
the meaning of the “low” setting in smtpd_tls_ciphers,
smtpd_tls_mandatory_ciphers, smtp_tls_ciphers, smtp_tls_mandatory_ciphers,
lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers. You are strongly
encouraged not to change this setting.

This feature is available in Postfix 2.3 and later.


(default: see “postconf -d” output)

The OpenSSL cipherlist for “medium” or higher grade ciphers. This
defines the meaning of the “medium” setting in smtpd_tls_ciphers,
smtpd_tls_mandatory_ciphers, smtp_tls_ciphers, smtp_tls_mandatory_ciphers,
lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers. This is the
default cipherlist for mandatory TLS encryption in the TLS client
(with anonymous ciphers disabled when verifying server certificates).
This is the default cipherlist for opportunistic TLS with Postfix
releases after the middle of 2022. You are strongly encouraged not
to change this setting.

This feature is available in Postfix 2.3 and later.


(default: eNULL:!aNULL)

The OpenSSL cipherlist for “NULL” grade ciphers that provide
authentication without encryption. This defines the meaning of the “null”
setting in smtpd_tls_mandatory_ciphers, smtp_tls_mandatory_ciphers and
lmtp_tls_mandatory_ciphers. You are strongly encouraged not to
change this setting.

This feature is available in Postfix 2.3 and later.


(default: no)

With SSLv3 and later, use the Postfix SMTP server’s cipher
preference order instead of the remote client’s cipher preference
order.

By default, the OpenSSL server selects the client’s most preferred
cipher that the server supports. With SSLv3 and later, the server may
choose its own most preferred cipher that is supported (offered) by
the client. Setting “tls_preempt_cipherlist = yes” enables server cipher
preferences.

While server cipher selection may in some cases lead to a more secure
or performant cipher choice, there is some risk of interoperability
issues. In the past, some SSL clients have listed lower priority ciphers
that they did not implement correctly. If the server chooses a cipher
that the client prefers less, it may select a cipher whose client
implementation is flawed. Most notably Windows 2003 Microsoft
Exchange servers have flawed implementations of DES-CBC3-SHA, which
OpenSSL considers stronger than RC4-SHA. Enabling server cipher-suite
selection may create interoperability issues with Windows 2003
Microsoft Exchange clients.

This feature is available in Postfix 2.8 and later, in combination
with OpenSSL 0.9.7 and later.


(default: 32)

The number of bytes that tlsmgr(8) reads from $tls_random_source
when (re)seeding the in-memory pseudo random number generator (PRNG)
pool. The default of 32 bytes (256 bits) is good enough for 128bit
symmetric keys. If using EGD or a device file, a maximum of 255
bytes is read.

This feature is available in Postfix 2.2 and later.


(default: see “postconf -d” output)

Name of the pseudo random number generator (PRNG) state file
that is maintained by tlsmgr(8). The file is created when it does
not exist, and its length is fixed at 1024 bytes.

As of version 2.5, Postfix no longer uses root privileges when
opening this file, and the default file location was changed from
${config_directory}/prng_exch to ${data_directory}/prng_exch. As
a migration aid, an attempt to open the file under a non-Postfix
directory is redirected to the Postfix-owned data_directory, and a
warning is logged.

This feature is available in Postfix 2.2 and later.


(default: 3600s)

The time between attempts by tlsmgr(8) to save the state of
the pseudo random number generator (PRNG) to the file specified
with $tls_random_exchange_name.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.2 and later.


(default: 3600s)

The maximal time between attempts by tlsmgr(8) to re-seed the
in-memory pseudo random number generator (PRNG) pool from external
sources. The actual time between re-seeding attempts is calculated
using the PRNG, and is between 0 and the time specified.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.2 and later.


(default: see “postconf -d” output)

The external entropy source for the in-memory tlsmgr(8) pseudo
random number generator (PRNG) pool. Be sure to specify a non-blocking
source. If this source is not a regular file, the entropy source
type must be prepended: egd:/path/to/egd_socket for a source with
EGD compatible socket interface, or dev:/path/to/device for a
device file.

Note: on OpenBSD systems specify dev:/dev/arandom when dev:/dev/urandom
gives timeout errors.

This feature is available in Postfix 2.2 and later.


(default: empty)

Optional lookup tables that map names received from remote SMTP
clients via the TLS Server Name Indication (SNI) extension to the
appropriate keys and certificate chains. This parameter is implemented
in the Postfix TLS library, and applies to both smtpd(8) and the SMTP
server mode of tlsproxy(8).

When this parameter is non-empty, the Postfix SMTP server enables
SNI extension processing, and logs SNI values that are invalid or
don’t match an entry in the specified tables. When an entry
does match, the SNI name is logged as part of the connection summary
at log levels 1 and higher.

The lookup key is either the verbatim SNI domain name or an
ancestor domain prefixed with a leading dot. For internationalized
domains, the lookup key must be in IDNA 2008 A-label form (as
required in the TLS SNI extension).

The syntax of the lookup value is the same as with the
smtp_tls_chain_files parameter (see there for additional details),
but here scoped to just TLS connections in which the client sends
a matching SNI domain name.

Example:

/etc/postfix/main.cf:
    #
    # The indexed SNI table must be created with "postmap -F"
    #
    indexed = ${default_database_type}:${config_directory}/
    tls_server_sni_maps = ${indexed}sni

/etc/postfix/sni:
    #
    # The example.com domain has both an RSA and ECDSA certificate
    # chain.  The chain files MUST start with the private key,
    # with the certificate chain next, starting with the leaf
    # (server) certificate, and then the issuer certificates.
    #
    example.com /etc/postfix/sni-chains/rsa2048.example.com.pem,
                /etc/postfix/sni-chains/ecdsa-p256.example.com.pem
    #
    # The example.net domain has a wildcard certificate, and two
    # additional DNS names.  So its certificate chain is also used
    # with any subdomain, plus the additional names.
    #
    example.net /etc/postfix/sni-chains/example.net.pem
    .example.net /etc/postfix/sni-chains/example.net.pem
    example.info /etc/postfix/sni-chains/example.net.pem
    example.org /etc/postfix/sni-chains/example.net.pem

Note that the SNI lookup tables should also have entries for
the domains that correspond to the Postfix SMTP server’s default
certificate(s). This ensures that the remote SMTP client’s TLS SNI
extension gets a positive response when it specifies one of the
Postfix SMTP server’s default domains, and ensures that the Postfix
SMTP server will not log an SNI name mismatch for such a domain.
The Postfix SMTP server’s default certificates are then only used
when the client sends no SNI or when it sends SNI with a domain
that the server knows no certificate(s) for.

The mapping from an SNI domain name to a certificate chain is indirect. In
the input source files for “cdb”, “hash”, “btree” or other tables that are
converted to on-disk indexed files via postmap(1), the value specified for each
key is a list of filenames. When postmap(1) is used with the -F option,
the generated table stores for each lookup key the base64-encoded contents of
the associated files. When querying tables via postmap -Fq, the table
value is decoded from base64, yielding the original file content, plus a new
line.

With “regexp”, “pcre”, “inline”, “texthash”, “static” and similar
tables that are interpreted at run-time, and don’t have a separate
source format, the table value is again a list files, that are loaded
into memory when the table is opened.

With tables whose content is managed outside of Postfix, such
as LDAP, MySQL, PostgreSQL, socketmap and tcp, the value must be a
concatenation of the desired PEM keys and certificate chains, that
is then further encoded to yield a single-line base64 string.
Creation of such tables and secure storage (the value includes
private key material) are outside the responsibility of Postfix.

With “socketmap” and “tcp” the data will be transmitted in the clear, and
there is no query access control, so these are generally unsuitable for storing
SNI chains. With LDAP and SQL, you should restrict read access and use TLS to
protect the sensitive data in transit.

Typically there is only one private key and its chain of certificates
starting with the “leaf” certificate corresponding to that key, and
continuing with the appropriate intermediate issuer CA certificates,
with each certificate ideally followed by its issuer. Servers
that have keys and certificates for more than one algorithm (e.g.
both an RSA key and an ECDSA key, or even RSA, ECDSA and Ed25519)
can use multiple chains concatenated together, with the key always
listed before the corresponding certificates.

This feature is available in Postfix 3.4 and later.


(default: Postfix ≥ 3.0: aes-256-cbc, Postfix < 3.0: aes-128-cbc)

Algorithm used to encrypt RFC5077 TLS session tickets. This
algorithm must use CBC mode, have a 128-bit block size, and must
have a key length between 128 and 256 bits. The default is
aes-256-cbc. Overriding the default to choose a different algorithm
is discouraged.

Setting this parameter empty disables session ticket support
in the Postfix SMTP server. Another way to disable session ticket
support is via the tls_ssl_options parameter.

This feature is available in Postfix 3.0 and later.


(default: empty)

List or bit-mask of OpenSSL options to enable.

The OpenSSL toolkit provides a set of options that applications
can enable to tune the OpenSSL behavior. Some of these work around
bugs in other implementations and are on by default. You can use
the tls_disable_workarounds parameter to selectively disable some
or all of the bug work-arounds, making OpenSSL more strict at the
cost of non-interoperability with SSL clients or servers that exhibit
the bugs.

Other options are off by default, and typically enable or disable
features rather than bug work-arounds. These may be turned on (with
care) via the tls_ssl_options parameter. The value is a white-space
or comma separated list of named options chosen from the list below.
The names are not case-sensitive, you can use lower-case if you
prefer. The upper case values below match the corresponding macro
name in the ssl.h header file with the SSL_OP_ prefix removed. It
is possible that your OpenSSL version includes new options added
after your Postfix source code was last updated, in that case you
can only enable one of these via the hexadecimal syntax below.

You should only enable features via the hexadecimal mask when
the need to control the feature is critical (to deal with a new
vulnerability or a serious interoperability problem). Postfix DOES
NOT promise backwards compatible behavior with respect to the mask
bits. A feature enabled via the mask in one release may be enabled
by other means in a later release, and the mask bit will then be
ignored. Therefore, use of the hexadecimal mask is only a temporary
measure until a new Postfix or OpenSSL release provides a better
solution.

If the value of the parameter is a hexadecimal long integer
starting with “0x”, the options corresponding to the bits specified
in its value are enabled (see openssl/ssl.h and SSL_CTX_set_options(3)).
You can only enable options not already controlled by other Postfix
settings. For example, you cannot disable protocols or enable
server cipher preference. Do not attempt to enable all features by
specifying 0xFFFFFFFF, this is unlikely to be a good idea. Some
bug work-arounds are also valid here, allowing them to be re-enabled
if/when they’re no longer enabled by default. The supported values
include:

ENABLE_MIDDLEBOX_COMPAT
Postfix ≥ 3.4. See
SSL_CTX_set_options(3).
LEGACY_SERVER_CONNECT
See SSL_CTX_set_options(3).
NO_TICKET
Enabled by default when needed in
fully-patched Postfix ≥ 2.7. Not needed at all for Postfix ≥
2.11, unless for some reason you do not want to support TLS session
resumption. Best not set explicitly. See SSL_CTX_set_options(3).
NO_COMPRESSION
Disable SSL compression even if
supported by the OpenSSL library. Compression is CPU-intensive,
and compression before encryption does not always improve security.
NO_RENEGOTIATION
Postfix ≥ 3.4. This can
reduce opportunities for a potential CPU exhaustion attack. See
SSL_CTX_set_options(3).
NO_SESSION_RESUMPTION_ON_RENEGOTIATION
Postfix
≥ 3.4. See SSL_CTX_set_options(3).
PRIORITIZE_CHACHA
Postfix ≥ 3.4. See SSL_CTX_set_options(3).

This feature is available in Postfix 2.11 and later.


(default: yes)

Match multiple DNS labels with “*” in wildcard certificates.

Some mail service providers prepend the customer domain name
to a base domain for which they have a wildcard TLS certificate.
For example, the MX records for example.com hosted by example.net
may be:

example.com. IN MX 0 example.com.mx1.example.net.
example.com. IN MX 0 example.com.mx2.example.net.

and the TLS certificate may be for “*.example.net”. The “*”
then corresponds with multiple labels in the mail server domain
name. While multi-label wildcards are not widely supported, and
are not blessed by any standard, there is little to be gained by
disallowing their use in this context.

Notes:

This feature is available in Postfix 2.11 and later.


(default: tlsmgr)

The name of the tlsmgr(8) service entry in master.cf. This
service maintains TLS session caches and other information in support
of TLS.

This feature is available in Postfix 2.11 and later.


(default: $smtp_tls_CAfile)

A file containing CA certificates of root CAs trusted to sign
either remote TLS server certificates or intermediate CA certificates.
See smtp_tls_CAfile for further details.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_CApath)

Directory with PEM format Certification Authority certificates
that the Postfix tlsproxy(8) client uses to verify a remote TLS
server certificate. See smtp_tls_CApath for further details.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_cert_file)

File with the Postfix tlsproxy(8) client RSA certificate in PEM
format. See smtp_tls_cert_file for further details. The preferred way
to configure tlsproxy client keys and certificates is via the
tlsproxy_client_chain_files” parameter.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_chain_files)

Files with the Postfix tlsproxy(8) client keys and certificate
chains in PEM format. See smtp_tls_chain_files for further details.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_dcert_file)

File with the Postfix tlsproxy(8) client DSA certificate in PEM
format. See smtp_tls_dcert_file for further details. DSA is obsolete and
should not be used.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_dkey_file)

File with the Postfix tlsproxy(8) client DSA private key in PEM
format. See smtp_tls_dkey_file for further details. DSA is obsolete and
should not be used.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_eccert_file)

File with the Postfix tlsproxy(8) client ECDSA certificate in PEM
format. See smtp_tls_eccert_file for further details. The preferred way
to configure tlsproxy client keys and certificates is via the
tlsproxy_client_chain_files” parameter.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_eckey_file)

File with the Postfix tlsproxy(8) client ECDSA private key in PEM
format. See smtp_tls_eckey_file for further details. The preferred way
to configure tlsproxy client keys and certificates is via the
tlsproxy_client_chain_files” parameter.

This feature is available in Postfix 3.4 and later.


(default: $smtp_enforce_tls)

Enforcement mode: require that SMTP servers use TLS encryption.
See smtp_enforce_tls for further details. Use
tlsproxy_client_security_level instead.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_fingerprint_digest)

The message digest algorithm used to construct remote TLS server
certificate fingerprints. See smtp_tls_fingerprint_digest for
further details.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_key_file)

File with the Postfix tlsproxy(8) client RSA private key in PEM
format. See smtp_tls_key_file for further details. The preferred way to
configure tlsproxy client keys and certificates is via the
tlsproxy_client_chain_files” parameter.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_security_level)

The default TLS security level for the Postfix tlsproxy(8)
client. See smtp_tls_security_level for further details.

This feature is available in Postfix 3.4 – 3.6. It was
renamed to tlsproxy_client_security_level in Postfix 3.7.


(default: $smtp_tls_loglevel)

Enable additional Postfix tlsproxy(8) client logging of TLS
activity. See smtp_tls_loglevel for further details.

This feature is available in Postfix 3.4 and later.


(default: smtp_tls_loglevel)

The name of the parameter that provides the tlsproxy_client_loglevel
value.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_per_site)

Optional lookup tables with the Postfix tlsproxy(8) client TLS
usage policy by next-hop destination and by remote TLS server
hostname. See smtp_tls_per_site for further details.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_policy_maps)

Optional lookup tables with the Postfix tlsproxy(8) client TLS
security policy by next-hop destination. See smtp_tls_policy_maps
for further details.

This feature is available in Postfix 3.4 – 3.6. It was
renamed to tlsproxy_client_policy_maps in Postfix 3.7.


(default: $smtp_tls_policy_maps)

Optional lookup tables with the Postfix tlsproxy(8) client TLS
security policy by next-hop destination. See smtp_tls_policy_maps
for further details.

This feature is available in Postfix 3.7 and later. It
was previously called tlsproxy_client_policy.


(default: $smtp_tls_scert_verifydepth)

The verification depth for remote TLS server certificates.
See smtp_tls_scert_verifydepth for further details.

This feature is available in Postfix 3.4 and later.


(default: $smtp_tls_security_level)

The default TLS security level for the Postfix tlsproxy(8)
client. See smtp_tls_security_level for further details.

This feature is available in Postfix 3.7 and later. It
was previously called tlsproxy_client_level.


(default: $smtp_use_tls)

Opportunistic mode: use TLS when a remote server announces TLS
support. See smtp_use_tls for further details. Use
tlsproxy_client_security_level instead.

This feature is available in Postfix 3.4 and later.


(default: $smtpd_enforce_tls)

Mandatory TLS: announce STARTTLS support to remote SMTP clients, and
require that clients use TLS encryption. See smtpd_enforce_tls for
further details. Use tlsproxy_tls_security_level instead.

This feature is available in Postfix 2.8 and later.


(default: tlsproxy)

The name of the tlsproxy(8) service entry in master.cf. This
service performs plaintext <=> TLS ciphertext conversion.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_CAfile)

A file containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or intermediate
CA certificates. See smtpd_tls_CAfile for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_CApath)

A directory containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or intermediate
CA certificates. See smtpd_tls_CApath for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_always_issue_session_ids)

Force the Postfix tlsproxy(8) server to issue a TLS session id,
even when TLS session caching is turned off. See
smtpd_tls_always_issue_session_ids for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_ask_ccert)

Ask a remote SMTP client for a client certificate. See
smtpd_tls_ask_ccert for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_ccert_verifydepth)

The verification depth for remote SMTP client certificates. A
depth of 1 is sufficient if the issuing CA is listed in a local CA
file. See smtpd_tls_ccert_verifydepth for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_cert_file)

File with the Postfix tlsproxy(8) server RSA certificate in PEM
format. This file may also contain the Postfix tlsproxy(8) server
private RSA key. See smtpd_tls_cert_file for further details. With
Postfix ≥ 3.4 the preferred way to configure tlsproxy server keys and
certificates is via the “tlsproxy_tls_chain_files” parameter.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_chain_files)

Files with the Postfix tlsproxy(8) server keys and certificate
chains in PEM format. See smtpd_tls_chain_files for further details.

This feature is available in Postfix 3.4 and later.


(default: $smtpd_tls_ciphers)

The minimum TLS cipher grade that the Postfix tlsproxy(8) server
will use with opportunistic TLS encryption. See smtpd_tls_ciphers
for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_dcert_file)

File with the Postfix tlsproxy(8) server DSA certificate in PEM
format. This file may also contain the Postfix tlsproxy(8) server
private DSA key. DSA is obsolete and should not be used. See
smtpd_tls_dcert_file for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_dh1024_param_file)

File with DH parameters that the Postfix tlsproxy(8) server
should use with non-export EDH ciphers. See smtpd_tls_dh1024_param_file
for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_dh512_param_file)

File with DH parameters that the Postfix tlsproxy(8) server
should use with export-grade EDH ciphers. See smtpd_tls_dh512_param_file
for further details. The default SMTP server cipher grade is
“medium” with Postfix releases after the middle of 2022, and as a
result export-grade cipher suites are by default not used.

With Postfix ≥ 3.6 export-grade Diffie-Hellman key exchange
is no longer supported, and this parameter is silently ignored.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_dkey_file)

File with the Postfix tlsproxy(8) server DSA private key in PEM
format. This file may be combined with the Postfix tlsproxy(8) server
DSA certificate file specified with $smtpd_tls_dcert_file. DSA is
obsolete and should not be used. See smtpd_tls_dkey_file for further
details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_eccert_file)

File with the Postfix tlsproxy(8) server ECDSA certificate in PEM
format. This file may also contain the Postfix tlsproxy(8) server
private ECDSA key. See smtpd_tls_eccert_file for further details. With
Postfix ≥ 3.4 the preferred way to configure tlsproxy server keys and
certificates is via the “tlsproxy_tls_chain_files” parameter.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_eckey_file)

File with the Postfix tlsproxy(8) server ECDSA private key in PEM
format. This file may be combined with the Postfix tlsproxy(8) server
ECDSA certificate file specified with $smtpd_tls_eccert_file. See
smtpd_tls_eckey_file for further details. With Postfix ≥ 3.4 the
preferred way to configure tlsproxy server keys and certificates is via
the “tlsproxy_tls_chain_files” parameter.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_eecdh_grade)

The Postfix tlsproxy(8) server security grade for ephemeral
elliptic-curve Diffie-Hellman (EECDH) key exchange. See
smtpd_tls_eecdh_grade for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_exclude_ciphers)

List of ciphers or cipher types to exclude from the tlsproxy(8)
server cipher list at all TLS security levels. See
smtpd_tls_exclude_ciphers for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_fingerprint_digest)

The message digest algorithm to construct remote SMTP
client-certificate
fingerprints. See smtpd_tls_fingerprint_digest for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_key_file)

File with the Postfix tlsproxy(8) server RSA private key in PEM
format. This file may be combined with the Postfix tlsproxy(8) server
RSA certificate file specified with $smtpd_tls_cert_file. See
smtpd_tls_key_file for further details. With Postfix ≥ 3.4 the
preferred way to configure tlsproxy server keys and certificates is via
the “tlsproxy_tls_chain_files” parameter.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_loglevel)

Enable additional Postfix tlsproxy(8) server logging of TLS
activity. Each logging level also includes the information that
is logged at a lower logging level. See smtpd_tls_loglevel for
further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_mandatory_ciphers)

The minimum TLS cipher grade that the Postfix tlsproxy(8) server
will use with mandatory TLS encryption. See smtpd_tls_mandatory_ciphers
for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_mandatory_exclude_ciphers)

Additional list of ciphers or cipher types to exclude from the
tlsproxy(8) server cipher list at mandatory TLS security levels.
See smtpd_tls_mandatory_exclude_ciphers for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_mandatory_protocols)

The SSL/TLS protocols accepted by the Postfix tlsproxy(8) server
with mandatory TLS encryption. If the list is empty, the server
supports all available SSL/TLS protocol versions. See
smtpd_tls_mandatory_protocols for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_protocols)

List of TLS protocols that the Postfix tlsproxy(8) server will
exclude or include with opportunistic TLS encryption. See
smtpd_tls_protocols for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_req_ccert)

With mandatory TLS encryption, require a trusted remote SMTP
client certificate in order to allow TLS connections to proceed.
See smtpd_tls_req_ccert for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_security_level)

The SMTP TLS security level for the Postfix tlsproxy(8) server;
when a non-empty value is specified, this overrides the obsolete
parameters smtpd_use_tls and smtpd_enforce_tls. See
smtpd_tls_security_level for further details.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_tls_session_cache_timeout)

Obsolete expiration time of Postfix tlsproxy(8) server TLS session
cache information. Since the cache is shared with smtpd(8) and managed
by tlsmgr(8), there is only one expiration time for the SMTP server cache
shared by all three services, namely smtpd_tls_session_cache_timeout.

This feature is available in Postfix 2.8 and later.


(default: $smtpd_use_tls)

Opportunistic TLS: announce STARTTLS support to remote SMTP clients,
but do not require that clients use TLS encryption. See smtpd_use_tls
for further details. Use tlsproxy_tls_security_level instead.

This feature is available in Postfix 2.8 and later.


(default: 10s)

How much time a tlsproxy(8) process may take to process local
or remote I/O before it is terminated by a built-in watchdog timer.
This is a safety mechanism that prevents tlsproxy(8) from becoming
non-responsive due to a bug in Postfix itself or in system software.
To avoid false alarms and unnecessary cache corruption this limit
cannot be set under 10s.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.8 and later


(default: trace)

The name of the trace service. This service is implemented by the
bounce(8) daemon and maintains a record
of mail deliveries and produces a mail delivery report when verbose
delivery is requested with “sendmail -v“.

This feature is available in Postfix 2.1 and later.


(default: $default_delivery_slot_cost)

A transport-specific override for the default_delivery_slot_cost
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: transport_delivery_slot_cost parameters will not
show up in “postconf” command output before Postfix version 2.9.
This limitation applies to many parameters whose name is a combination
of a master.cf service name and a built-in suffix (in this case:
“_delivery_slot_cost”).


(default: $default_delivery_slot_discount)

A transport-specific override for the default_delivery_slot_discount
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: transport_delivery_slot_discount parameters will
not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_delivery_slot_discount”).


(default: $default_delivery_slot_loan)

A transport-specific override for the default_delivery_slot_loan
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: transport_delivery_slot_loan parameters will not
show up in “postconf” command output before Postfix version 2.9.
This limitation applies to many parameters whose name is a combination
of a master.cf service name and a built-in suffix (in this case:
“_delivery_slot_loan”).


(default: $default_destination_concurrency_failed_cohort_limit)

A transport-specific override for the
default_destination_concurrency_failed_cohort_limit parameter value,
where transport is the master.cf name of the message delivery
transport.

Note: some transport_destination_concurrency_failed_cohort_limit
parameters will not show up in “postconf” command output before
Postfix version 2.9. This limitation applies to many parameters
whose name is a combination of a master.cf service name and a
built-in suffix (in this case:
“_destination_concurrency_failed_cohort_limit”).

This feature is available in Postfix 2.5 and later.


(default: $default_destination_concurrency_limit)

A transport-specific override for the
default_destination_concurrency_limit parameter value, where
transport is the master.cf name of the message delivery
transport.

Note: some transport_destination_concurrency_limit
parameters will not show up in “postconf” command output before
Postfix version 2.9. This limitation applies to many parameters
whose name is a combination of a master.cf service name and a
built-in suffix (in this case: “_destination_concurrency_limit”).


(default: $default_destination_concurrency_negative_feedback)

A transport-specific override for the
default_destination_concurrency_negative_feedback parameter value,
where transport is the master.cf name of the message delivery
transport.

Note: some transport_destination_concurrency_negative_feedback
parameters will not show up in “postconf” command output before
Postfix version 2.9. This limitation applies to many parameters
whose name is a combination of a master.cf service name and a
built-in suffix (in this case:
“_destination_concurrency_negative_feedback”).

This feature is available in Postfix 2.5 and later.


(default: $default_destination_concurrency_positive_feedback)

A transport-specific override for the
default_destination_concurrency_positive_feedback parameter value,
where transport is the master.cf name of the message delivery
transport.

Note: some transport_destination_concurrency_positive_feedback
parameters will not show up in “postconf” command output before
Postfix version 2.9. This limitation applies to many parameters
whose name is a combination of a master.cf service name and a
built-in suffix (in this case:
“_destination_concurrency_positive_feedback”).

This feature is available in Postfix 2.5 and later.


(default: $default_destination_rate_delay)

A transport-specific override for the default_destination_rate_delay
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: some transport_destination_rate_delay parameters
will not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_destination_rate_delay”).

This feature is available in Postfix 2.5 and later.


(default: $default_destination_recipient_limit)

A transport-specific override for the
default_destination_recipient_limit parameter value, where
transport is the master.cf name of the message delivery
transport.

Note: some transport_destination_recipient_limit parameters
will not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_destination_recipient_limit”).


(default: $default_extra_recipient_limit)

A transport-specific override for the default_extra_recipient_limit
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: transport_extra_recipient_limit parameters will
not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_extra_recipient_limit”).


(default: $initial_destination_concurrency)

A transport-specific override for the initial_destination_concurrency
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: some transport_initial_destination_concurrency
parameters will not show up in “postconf” command output before
Postfix version 2.9. This limitation applies to many parameters
whose name is a combination of a master.cf service name and a
built-in suffix (in this case: “_initial_destination_concurrency”).

This feature is available in Postfix 2.5 and later.


(default: empty)

Optional lookup tables with mappings from recipient address to
(message delivery transport, next-hop destination). See transport(5)
for details.

Specify zero or more “type:table” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found. If you use this
feature with local files, run “postmap /etc/postfix/transport
after making a change.

Pattern matching of domain names is controlled by the presence
or absence of “transport_maps” in the parent_domain_matches_subdomains
parameter value.

For safety reasons, as of Postfix 2.3 this feature does not
allow $number substitutions in regular expression maps.

Examples:

transport_maps = dbm:/etc/postfix/transport
transport_maps = hash:/etc/postfix/transport

(default: $default_minimum_delivery_slots)

A transport-specific override for the default_minimum_delivery_slots
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: transport_minimum_delivery_slots parameters will
not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_minimum_delivery_slots”).


(default: $default_recipient_limit)

A transport-specific override for the default_recipient_limit
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: some transport_recipient_limit parameters will not
show up in “postconf” command output before Postfix version 2.9.
This limitation applies to many parameters whose name is a combination
of a master.cf service name and a built-in suffix (in this case:
“_recipient_limit”).


(default: $default_recipient_refill_delay)

A transport-specific override for the default_recipient_refill_delay
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: transport_recipient_refill_delay parameters will
not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_recipient_refill_delay”).

This feature is available in Postfix 2.4 and later.


(default: $default_recipient_refill_limit)

A transport-specific override for the default_recipient_refill_limit
parameter value, where transport is the master.cf name of
the message delivery transport.

Note: transport_recipient_refill_limit parameters will
not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_recipient_refill_limit”).

This feature is available in Postfix 2.4 and later.


(default: 60s)

The time between attempts by the Postfix queue manager to contact
a malfunctioning message delivery transport.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: $command_time_limit)

A transport-specific override for the command_time_limit parameter
value, where transport is the master.cf name of the message
delivery transport.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

Note: transport_time_limit parameters will not show up
in “postconf” command output before Postfix version 2.9. This
limitation applies to many parameters whose name is a combination
of a master.cf service name and a built-in suffix (in this case:
“_time_limit”).


(default: $default_transport_rate_delay)

A transport-specific override for the default_transport_rate_delay
parameter value, where the initial transport in the parameter
name is the master.cf name of the message delivery transport.

Specify a non-negative time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

Note: transport_transport_rate_delay parameters will
not show up in “postconf” command output before Postfix version
2.9. This limitation applies to many parameters whose name is a
combination of a master.cf service name and a built-in suffix (in
this case: “_transport_rate_delay”).


(default: 10s)

The time limit for sending a trigger to a Postfix daemon (for
example, the pickup(8) or qmgr(8) daemon). This time limit prevents
programs from getting stuck when the mail system is under heavy
load.

Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). Time units: s
(seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).


(default: see “postconf -d” output)

Message header that the Postfix cleanup(8) server inserts when a
message contains no To: or Cc: message header. With Postfix 2.8
and later, the default value is empty. With Postfix 2.4-2.7,
specify an empty value to disable this feature.

Example:

# Default value before Postfix 2.8.
# Note: the ":" and ";" are both required.
undisclosed_recipients_header = To: undisclosed-recipients:;

(default: 450)

The numerical response code when the Postfix SMTP server rejects a
sender or recipient address because its domain is unknown. This
is one of the possible replies from the restrictions
reject_unknown_sender_domain and reject_unknown_recipient_domain.

Do not change this unless you have a complete understanding of RFC 5321.


(default: $reject_tempfail_action)

The Postfix SMTP server’s action when reject_unknown_sender_domain
or reject_unknown_recipient_domain fail due to a temporary error
condition. Specify “defer” to defer the remote SMTP client request
immediately. With the default “defer_if_permit” action, the Postfix
SMTP server continues to look for opportunities to reject mail, and
defers the client request only if it would otherwise be accepted.

This feature is available in Postfix 2.6 and later.


(default: 450)

The numerical Postfix SMTP server response code when a client
without valid address <=> name mapping is rejected by the
reject_unknown_client_hostname restriction. The SMTP server always replies
with 450 when the mapping failed due to a temporary error condition.

Do not change this unless you have a complete understanding of RFC 5321.


(default: $reject_tempfail_action)

The Postfix SMTP server’s action when reject_unknown_helo_hostname
fails due to a temporary error condition. Specify “defer” to defer
the remote SMTP client request immediately. With the default
defer_if_permit” action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted.

This feature is available in Postfix 2.6 and later.


(default: 450)

The numerical Postfix SMTP server response code when the hostname
specified with the HELO or EHLO command is rejected by the
reject_unknown_helo_hostname restriction.

Do not change this unless you have a complete understanding of RFC 5321.


(default: 550)

The numerical Postfix SMTP server response code when a recipient
address is local, and $local_recipient_maps specifies a list of
lookup tables that does not match the recipient. A recipient
address is local when its domain matches $mydestination,
$proxy_interfaces or $inet_interfaces.

The default setting is 550 (reject mail) but it is safer to initially
use 450 (try again later) so you have time to find out if your
local_recipient_maps settings are OK.

Example:

unknown_local_recipient_reject_code = 450

This feature is available in Postfix 2.0 and later.


(default: 550)

The numerical Postfix SMTP server reply code when a recipient
address matches $relay_domains, and relay_recipient_maps specifies
a list of lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.


(default: 550)

The Postfix SMTP server reply code when a recipient address matches
$virtual_alias_domains, and $virtual_alias_maps specifies a list
of lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.


(default: 550)

The Postfix SMTP server reply code when a recipient address matches
$virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list
of lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.


(default: 450)

The numerical Postfix SMTP server response when a recipient address
probe fails due to a temporary error condition.

Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.

Do not change this unless you have a complete understanding of RFC 5321.

This feature is available in Postfix 2.6 and later.


(default: 450)

The numerical Postfix SMTP server response when a recipient address
is rejected by the reject_unverified_recipient restriction.

Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.

Do not change this unless you have a complete understanding of RFC 5321.

This feature is available in Postfix 2.1 and later.


(default: empty)

The Postfix SMTP server’s reply when rejecting mail with
reject_unverified_recipient. Do not include the numeric SMTP reply
code or the enhanced status code. By default, the response includes
actual address verification details.

Example:

unverified_recipient_reject_reason = Recipient address lookup failed

This feature is available in Postfix 2.6 and later.


(default: $reject_tempfail_action)

The Postfix SMTP server’s action when reject_unverified_recipient
fails due to a temporary error condition. Specify “defer” to defer
the remote SMTP client request immediately. With the default
defer_if_permit” action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted.

This feature is available in Postfix 2.6 and later.


(default: 450)

The numerical Postfix SMTP server response code when a sender address
probe fails due to a temporary error condition.

Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.

Do not change this unless you have a complete understanding of RFC 5321.

This feature is available in Postfix 2.6 and later.


(default: 450)

The numerical Postfix SMTP server response code when a recipient
address is rejected by the reject_unverified_sender restriction.

Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.

Do not change this unless you have a complete understanding of RFC 5321.

This feature is available in Postfix 2.1 and later.


(default: empty)

The Postfix SMTP server’s reply when rejecting mail with
reject_unverified_sender. Do not include the numeric SMTP reply
code or the enhanced status code. By default, the response includes
actual address verification details.

Example:

unverified_sender_reject_reason = Sender address lookup failed

This feature is available in Postfix 2.6 and later.


(default: $reject_tempfail_action)

The Postfix SMTP server’s action when reject_unverified_sender
fails due to a temporary error condition. Specify “defer” to defer
the remote SMTP client request immediately. With the default
defer_if_permit” action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted.

This feature is available in Postfix 2.6 and later.


(default: -= )

The characters Postfix accepts as VERP delimiter characters on the
Postfix sendmail(1) command line and in SMTP commands.

This feature is available in Postfix 1.1 and later.


(default: 1000)

The maximal length of an email address after virtual alias expansion.
This stops virtual aliasing loops that increase the address length
exponentially.

This feature is available in Postfix 3.0 and later.


(default: $virtual_alias_maps)

Postfix is the final destination for the specified list of virtual
alias domains, that is, domains for which all addresses are aliased
to addresses in other local or remote domains. The SMTP server
validates recipient addresses with $virtual_alias_maps and rejects
non-existent recipients. See also the virtual alias domain class
in the ADDRESS_CLASS_README file

This feature is available in Postfix 2.0 and later. The default
value is backwards compatible with Postfix version 1.1.

The default value is $virtual_alias_maps so that you can keep all
information about virtual alias domains in one place. If you have
many users, it is better to separate information that changes more
frequently (virtual address -> local or remote address mapping)
from information that changes less frequently (the list of virtual
domain names).

Specify a list of host or domain names, “/file/name” or
type:table” patterns, separated by commas and/or whitespace. A
“/file/name” pattern is replaced by its contents; a “type:table
lookup table is matched when a table entry matches a host or domain name
(the lookup result is ignored). Continue long lines by starting
the next line with whitespace. Specify “!pattern” to exclude a host
or domain name from the list. The form “!/file/name” is supported
only in Postfix version 2.4 and later.

See also the VIRTUAL_README and ADDRESS_CLASS_README documents
for further information.

Example:

virtual_alias_domains = virtual1.tld virtual2.tld

(default: 1000)

The maximal number of addresses that virtual alias expansion produces
from each original recipient.

This feature is available in Postfix 2.1 and later.


(default: $virtual_maps)

Optional lookup tables that alias specific mail addresses or domains
to other local or remote addresses. The table format and lookups
are documented in virtual(5). For an overview of Postfix address
manipulations see the ADDRESS_REWRITING_README document.

This feature is available in Postfix 2.0 and later. The default
value is backwards compatible with Postfix version 1.1.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.
Note: these lookups are recursive.

If you use this feature with indexed files, run “postmap
/etc/postfix/virtual
” after changing the file.

Examples:

virtual_alias_maps = dbm:/etc/postfix/virtual
virtual_alias_maps = hash:/etc/postfix/virtual

(default: 1000)

The maximal nesting depth of virtual alias expansion. Currently
the recursion limit is applied only to the left branch of the
expansion graph, so the depth of the tree can in the worst case
reach the sum of the expansion and recursion limits. This may
change in the future.

This feature is available in Postfix 2.1 and later.


(default: $default_delivery_status_filter)

Optional filter for the virtual(8) delivery agent to change the
delivery status code or explanatory text of successful or unsuccessful
deliveries. See default_delivery_status_filter for details.

This feature is available in Postfix 3.0 and later.


(default: $default_destination_concurrency_limit)

The maximal number of parallel deliveries to the same destination
via the virtual message delivery transport. This limit is enforced
by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.


(default: $default_destination_recipient_limit)

The maximal number of recipients per message for the virtual
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.

Setting this parameter to a value of 1 changes the meaning of
virtual_destination_concurrency_limit from concurrency per domain
into concurrency per recipient.


(default: empty)

Lookup tables with the per-recipient group ID for virtual(8) mailbox
delivery.

This parameter is specific to the virtual(8) delivery agent.
It does not apply when mail is delivered with a different mail
delivery program.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

In a lookup table, specify a left-hand side of “@domain.tld” to
match any user in the specified domain that does not have a specific
“user@domain.tld” entry.

When a recipient address has an optional address extension
(user foo@domain.tld), the virtual(8) delivery agent looks up
the full address first, and when the lookup fails, it looks up the
unextended address (user@domain.tld).

Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression
lookup tables, because that would open a security hole.

Note 2: for security reasons, the virtual(8) delivery agent will
silently ignore requests to use the proxymap(8) server. Instead
it will open the table directly. Before Postfix version 2.2, the
virtual(8) delivery agent will terminate with a fatal error.


(default: empty)

A prefix that the virtual(8) delivery agent prepends to all pathname
results from $virtual_mailbox_maps table lookups. This is a safety
measure to ensure that an out of control map doesn’t litter the
file system with mailboxes. While virtual_mailbox_base could be
set to “/”, this setting isn’t recommended.

This parameter is specific to the virtual(8) delivery agent.
It does not apply when mail is delivered with a different mail
delivery program.

Example:

virtual_mailbox_base = /var/mail

(default: $virtual_mailbox_maps)

Postfix is the final destination for the specified list of domains;
mail is delivered via the $virtual_transport mail delivery transport.
By default this is the Postfix virtual(8) delivery agent. The SMTP
server validates recipient addresses with $virtual_mailbox_maps
and rejects mail for non-existent recipients. See also the virtual
mailbox domain class in the ADDRESS_CLASS_README file.

This parameter expects the same syntax as the mydestination
configuration parameter.

This feature is available in Postfix 2.0 and later. The default
value is backwards compatible with Postfix version 1.1.


(default: 51200000)

The maximal size in bytes of an individual virtual(8) mailbox or
maildir file, or zero (no limit).

This parameter is specific to the virtual(8) delivery agent.
It does not apply when mail is delivered with a different mail
delivery program.


(default: see “postconf -d” output)

How to lock a UNIX-style virtual(8) mailbox before attempting
delivery. For a list of available file locking methods, use the
postconf -l” command.

This parameter is specific to the virtual(8) delivery agent.
It does not apply when mail is delivered with a different mail
delivery program.

This setting is ignored with maildir style delivery, because
such deliveries are safe without application-level locks.

Note 1: the dotlock method requires that the recipient UID
or GID has write access to the parent directory of the recipient’s
mailbox file.

Note 2: the default setting of this parameter is system dependent.


(default: empty)

Optional lookup tables with all valid addresses in the domains that
match $virtual_mailbox_domains.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

In a lookup table, specify a left-hand side of “@domain.tld” to
match any user in the specified domain that does not have a specific
“user@domain.tld” entry.

With the default “virtual_mailbox_domains = $virtual_mailbox_maps“,
lookup tables also need entries with a left-hand side of “domain.tld”
to satisfy virtual_mailbox_domain lookups (the right-hand side is
required but will not be used).

The remainder of this text is specific to the virtual(8) delivery
agent. It does not apply when mail is delivered with a different
mail delivery program.

The virtual(8) delivery agent uses this table to look up the
per-recipient mailbox or maildir pathname. If the lookup result
ends in a slash (“/”), maildir-style delivery is carried out,
otherwise the path is assumed to specify a UNIX-style mailbox file.
Note that $virtual_mailbox_base is unconditionally prepended to
this path.

When a recipient address has an optional address extension
(user foo@domain.tld), the virtual(8) delivery agent looks up
the full address first, and when the lookup fails, it looks up the
unextended address (user@domain.tld).

Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression
lookup tables, because that would open a security hole.

Note 2: for security reasons, the virtual(8) delivery agent will
silently ignore requests to use the proxymap(8) server. Instead
it will open the table directly. Before Postfix version 2.2, the
virtual(8) delivery agent will terminate with a fatal error.


(default: empty)

Optional lookup tables with a) names of domains for which all
addresses are aliased to addresses in other local or remote domains,
and b) addresses that are aliased to addresses in other local or
remote domains. Available before Postfix version 2.0. With Postfix
version 2.0 and later, this is replaced by separate controls: virtual_alias_domains
and virtual_alias_maps.


(default: 100)

The minimum user ID value that the virtual(8) delivery agent accepts
as a result from $virtual_uid_maps table lookup. Returned
values less than this will be rejected, and the message will be
deferred.

This parameter is specific to the virtual(8) delivery agent.
It does not apply when mail is delivered with a different mail
delivery program.


(default: virtual)

The default mail delivery transport and next-hop destination for
final delivery to domains listed with $virtual_mailbox_domains.
This information can be overruled with the transport(5) table.

Specify a string of the form transport:nexthop, where transport
is the name of a mail delivery transport defined in master.cf.
The :nexthop destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent.

This feature is available in Postfix 2.0 and later.


(default: empty)

Lookup tables with the per-recipient user ID that the virtual(8)
delivery agent uses while writing to the recipient’s mailbox.

This parameter is specific to the virtual(8) delivery agent.
It does not apply when mail is delivered with a different mail
delivery program.

Specify zero or more “type:name” lookup tables, separated by
whitespace or comma. Tables will be searched in the specified order
until a match is found.

In a lookup table, specify a left-hand side of “@domain.tld”
to match any user in the specified domain that does not have a
specific “user@domain.tld” entry.

When a recipient address has an optional address extension
(user foo@domain.tld), the virtual(8) delivery agent looks up
the full address first, and when the lookup fails, it looks up the
unextended address (user@domain.tld).

Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression
lookup tables, because that would open a security hole.

Note 2: for security reasons, the virtual(8) delivery agent will
silently ignore requests to use the proxymap(8) server. Instead
it will open the table directly. Before Postfix version 2.2, the
virtual(8) delivery agent will terminate with a fatal error.

Без шифрования

а) если используем CentOS / Red Hat:

б) если используем Ubuntu / Debian:

apt-get install dovecot-imapd dovecot-pop3d

Открываем конфигурационный файл Postfix:

smtpd_sasl_path = private/auth smtpd_sasl_auth_enable = yes smtpd_sasl_type = dovecot smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination

* где smtpd_sasl_path — путь до плагина аутентификации по механизму SASL; smtpd_sasl_auth_enable — разрешает или запрещает аутентификацию по механизму SASL; smtpd_sasl_type — тип плагина, который используется для SASL-аутентификации; smtpd_relay_restrictions — правила разрешения и запрета использования MTA при пересылке.

Открываем настройки аутентификации в dovecot:

и приводим опцию service auth к следующему виду:

Настройка postfix с smtp-auth и tls

Postfix — агент передачи почты.

SMTP AUTH — продолжение протокола передачи почты посредством которого, клиент SMTP может войти, используя механизм аутентификации выбран. Модуль проверки подлинности является обязательным для представления серверов.

TLS —криптографический протокол, обеспечивающий защищённую передачу данных между узлами в сети Интернет.

Далее нужно отредактировать основной конфигурационный файл postfix.(вообще я рекомендую писать это непосредственно в файле /etc/postfix/main.cf , так как с помощью текстового редактора vim, можно подсвечивать синтаксис, это гораздо удобнее, нежели писать в командном интерпретаторе).

Пример записи непосредственно в файл:smtpd_sasl_local_domain =

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